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Issei has developed many relationships throughout the series, both within the Occult Research Club and the Three Factions. He has also attracted the attention of most of the female characters.

Rias Gremory
Rias is the woman who reincarnated Issei after Raynare killed him and the woman he loves. When she first summoned him, she treated him as a "special" case, knowing that he had a lot of potential. Issei was attracted to her like any other girl but disliked her for forbidding him from associating with Asia for being on the Fallen Angels side and saving her from them, that is until she realised that they were up to something shady in their town. After helping him save and resurrect Asia as well as killing the woman who murdered him, Issei began developing more respect and admiration for Rias to an eventual crush. In Volume 2, as time went on, she later started to fall in love with him and her love became deeper after he saved her from Riser and for recognizing her as an equal rather than an heir of Gremory or a Devil. She kissed Issei for the first time, following the latter's duel with Riser. She often gets jealous when other girls flirt with or tempt him, even saying that Issei belongs only to her. She loves him very much and is willing to do anything with him. In response, Issei will do anything to protect her, as he loves her just as much as she loves him.

To add to that, by Volume 3 Rias now usually sleeps next to him naked in his bed and joining him in the bath, showcasing her bold attempts to seduce him. For this reason, she says that she has no problem with letting Issei see her naked and even lets him touch her breasts from time to time. However she still gets angry whenever he plots something behind her back without her permission or knowledge and for that she felt it necessary to punish is with nearly a thousand demonic empowered spanks.

In Volume 5, Rias starts becoming Issei's source of power and motivation, more so whenever he touches her breasts, like when he poked her nipples which allowed him to achieve his Balance Breaker.

In Volume 6, Issei going berserk under the effects of Juggernaut Drive caused Rias to be distraught over the possibility of losing him. When coming to the conclusion that her breasts would cure him, she put up with the embarrassment when it meant saving him.

In Volume 7, Rias received her derogatory nicknames such as "Switch Princess" (Bikou) officially used in Issei's "Oppai Dragon", an underworld's children's television show and "Crimson Bust Princess" (Azazel). As Issei was nervous on the night before the battle with Loki, Rias comforted him as she snuggled next to him. She expressed her feelings that even though she hates those nicknames, she doesn't mind using her breasts for Issei's power ups, as she wants to be the source of his power and doesn't care if he is the Oppai Dragon. This act touched Issei to ease his nerves.

In Volume 8, Issei and Rias go through a ritual where they are tested to see if Issei is worthy of being a candidate for Rias' future husband. They both passed and although Issei remained oblivious to the situation, he had mentioned that he would like to marry Rias one day.

In Volume 10, Issei was given permission from Rias's mother to start a harem to keep the girls around him happy. During this time, Issei was struggling to overcome the trauma that was caused by Raynare. This trauma is the reason why he could not believe that the women around him would actually be attracted to him. This caused tension to form between Rias and Issei, such when she attempted make love to him he still referred to her as "President" and remained oblivious to how she feels towards him. That is until he proclaims his love for her in front of the audience during the Rating Game against Sairaorg Bael. He professed his love for her again at their club room and called Rias by her given for the first time, to which she cried tears of joy and confessed her love back.

After becoming Issei's girlfriend, Issei always assures Rias that she is the most important woman in his life, much to her happiness.

In Volume 11, as Issei began to slowly die due to Samuel's curse, he lamented over his regret that he couldn't return to them as promised but was glad enough that he was able to confess his love to Rias when he did.

By Volume 12, Rias was completely heartbroken by the news of Issei's death, but gained a great deal of hope when she found out that his spirit was still alive through his Evil Pieces. Upon his return, he felt joy being in Rias embrace and the sensation of her kiss once again.

In Volume 17, their relationship has improved to the extent that despite going out on a date with someone else, Rias chose to believe in Issei and the fact that he will still love her. At the end of the volume, Issei asks Rias if he could talk to her casually in private times, to which she happily replies yes.

In Volume 22, Rias was there to allow Issei to be promoted to High-Class devil, during the ritual in which she placed the crown on his head, which made Issei a King. Later the two become engaged when Issei proposes to Rias after her graduation ceremony, making her his first bride.

In Volume 25, while celebrating at the Hyoudou residence, following the defeat of Vidar, the girls (Asia, Xenovia, Irina, Akeno, Kuroka, Koneko, Rossweisse, and Rias) tell Issei to show his love for them which he does and tells them that every one of them is his bride. This statement reveals that Issei is now planning to marry all eight of them.

Later in True Volume 1, when their teams were both matched up against each other, the two promised to give it their very best in their upcoming fight. In the following volume, Rias even half jokingly stated that she would cancel their engagement if Issei where to go easy on her. During their date, when asked if he can defeat her, Issei replied that as her servant, he has sworn to become the strongest Pawn and that he wants her to watch over his progress as he intends to defeat her, much to her happiness as she swore to defeat him too.

Asia Argento
Issei is very protective of Asia ever since he met her, pitying the girl's suffering and was greatly saddened when she was killed by Raynare. Issei views Asia as a little sister that he needs to protect and is willing to fight anyone that tries to hurt her such as Raynare, Freed Sellzen and Diodora Astaroth. In fact, when Asia was supposedly killed by Shalba Beelzebub, the negative emotions of losing Asia made Issei enter the Juggernaut Drive and brutally mutilate him, nearly killing him. At one point, Akeno Himejima observed that Issei's feelings for Asia might be second only to his love for Rias.

Issei often has lecherous thoughts about her, but tries to block them, believing that he must protect her from everyone, including himself, and tries to think of her as a younger sister.

At the end of Volume 6 in the light novels, Asia kisses Issei, causing him to see her more as a woman than his younger sister. After that event, she became more bold and daring in their relationship, as it is implied that she gives him a good morning kiss almost every morning. She loves him greatly, as she became tearfully happy when their love prediction was favorable and declared that she wants to bear his child.

She became heartbroken and devastated when she thought that Issei had died, spending most of her time crying and planning to commit suicide to be with him, though she knew Issei would be upset if she did so, confused for not knowing what to do. When she learned that his spirit is alive, she cried loudly out of relief, joy and regained hope, embracing him when he returned. Asia desires to stay with Issei forever, even if it means becoming one of his peerage, which happens in Volume 22 when she became his official Bishop.

In Volume 23, Issei proposes to Asia, promising to make her happy and be by her side for eternity. Asia, filled with tears of joy, accepts Issei's proposal, making her his fifth bride.

In Volume 25, while celebrating at the Hyoudou residence, following the defeat of Vidar, the girls (Asia, Xenovia, Irina, Akeno, Kuroka, Koneko, Rossweisse, and Rias) tell Issei to show his love for them which he does and tells them that every one of them is his bride. This statement reveals that Issei is now planning to marry all eight of them.

In True Volume 2, during the Rating Game match, Asia showcased her bravery and devotion to Issei as his servant by willingly facing Crom Cruach in battle despite knowing she had not chance of victory in order to make Issei win the match by preserving his stamina for his confrontation with Rias. Even after Fafnir was defeated, she kept fighting, stating that as the servant and future wife of the Red Dragon Emperor Issei, she would keep fighting until the end, which impressed Crom Cruach.

Akeno Himejima
When Akeno first met Issei, she thought of him as a cute kouhai with whom she could spoil and flirt, but as time went on, she started to see that Issei was very kind and caring. She began show lustful attraction towards after witnessing his determination against Riser. His kind acts were fully shown when he defended Akeno against Kokabiel's insults towards her heritage which eventually cause her to completely fall in love with him in Volume 3. She isn't afraid to get into fights over him with the other girls as she loves him just as much as they do. She does get jealous when other girls get closer to him, though she is a lot calmer about it than Rias and the others.

In Volume 4, she would often make advances towards him, usually being more provocative than the other girls which annoyed Rias the most as the two fought throwing blasts at each other. Later Akeno would open up about her mixed blood heritage to Issei, despite his hatred toward Fallen Angels, Issei stated that he never hated Akeno, seeing her as his kind senpai, this only causes Akeno to further fall for Issei and embrace him and is fine being third in his heart after Rias and Asia, as she likes the idea of an affair.

In Volume 5, her antics become more bold as she also sneaks into his bed naked. Issei became the source of her motivation and was angered that at Sona's team beating in the Rating Game.

In Volume 6, under Koneko's suggestion, Issei asked Akeno on a date should she defeat Diodora's peerage as a way to motivate her.

In Volume 7, upon going on their date, she loses her "Onee-sama" aura around him and acted like a normal girl her age, which Issei admired alot. When the thought of Akeno someday getting a boyfriend popped into his head, Issei was determined to make the best of this so that he would be jealous of Issei. Their date eventually led to a street of love hotels while trying to escape their friends pursuing them, Issei was on board with going in having sex with Akeno when she assures him that she didn't mind, however their date came to an end when Odin and Akeno's estranged father arrived. During this time, Issei would learn about Akeno's past in more detail concerning her mothers death and how she blamed her father for it. Understanding her pain Issei attempts to help her overcome this, later going as far as to resist having sex with her as it would've further complicate things, instead he simply gave a gentle embrace, showing how serious she means to him. Near the end of the battle of Loki, Issei was able to reconcile with Akeno with her father, this led Akeno to both kiss and confess to Issei that she loves him in front all the other girls.

In Volume 10, during the preparations for the school festival, Akeno scolded him when he unknowingly hurt Rias' feelings by not calling her by her name and not acknowledging their relationship. She later came to comfort Issei when she figured out why Issei was unable to confess to Rias and would look at the ORC girls with frightened eyes, saying that she likes him and that as a Fallen Angel herself, she can replace Raynare who hurt him. She told him to have more confidence as she could not take another step forward in her relationship with him until he confessed to Rias, as she promised to stay with him forever. She later peeked at Issei's confession to Rias, saying that she can get serious about having an affair with him.

In Volume 12, she was heartbroken when she thought that Issei had died so much so that she disconnected herself from reality, remembering only the times that she spent with Issei, and cried terribly with her father as he comforted her. She, along with everyone else, later regained hope after finding out that Issei's spirit was alive, and she embraced him when he returned, begging him to never leave her again. She is psychologically dependent on Issei, as shown by her behavior after believing he was dead, and her display of anger when he lost in the Rating Game against Sona Sitri. Akeno gave an overwhelming killing intent towards Siegfried, who was a member of the group responsible for Issei's death, during their fated encounter on Ajuka Beelzebub's research centre's rooftop. Akeno was so overjoyed with tears when Issei returned to them, she hugged him asking to never leave again. Issei also knows that she is emotionally fragile, so he cares for her a great deal and has promised her that he will not die again or cause her any pain.

Akeno has stated that she would love to bear Issei's children during the visit of Millicas in the human world and several instances afterwards. She was depressed when Issei had to pretend to be the boyfriend of Rossweisse in front of the latter's grandmother in Volume 17, but soon cheered up when Rias told Issei that he would have to go on a date with her and Akeno after his ordeal with Rossweisse.

In Volume 22, Issei both confessed his love for her and proposed to her through the broadcast of the Rating Game between his team and Baraqiel's team, during his final fight with Baraqiel. After the events, Akeno has constantly been calling Issei "Darling" and started behaving like she is his wife, despite being only engaged to one another.

In Volume 23, Akeno would take even more bold actions such as calling Issei "Husband" or "Dear" and wash every part of his body when bathing together.

In Volume 25, while celebrating at the Hyoudou residence, following the defeat of Vidar, the girls (Asia, Xenovia, Irina, Akeno, Kuroka, Koneko, Rossweisse, and Rias) tell Issei to show his love for them which he does and tells them that every one of them is his bride. This statement reveals that Issei is now planning to marry all eight of them.

Akeno sometimes expresses jealousy whenever Rias' breast are used to assist Issei, which is why in True Volume 1, Akeno was glad that her breast were used for Issei's Pai Phone technique.

Koneko Toujou
At first, Koneko disliked Issei due to his lecherous mind and antics, but respected him after seeing his determination and tenacity for never giving up and also because of his willingness to go to great lengths to help a friend in need. Even though his methods got lecherous, she drew on his courage to help herself get stronger and braver. She would almost ridicule Issei or beat him up whenever she caught him attempting to commit perverted acts.

She started to develop feelings for him after he helped her overcome her fear of Senjutsu, as Issei told her he was not afraid of her powers and would stop her if she ever went out of control. After that, she began sitting nowhere else but on Issei's lap, and began seducing him like all the other girls in the harem. While Koneko still dislikes his perverted ways, she appears to still love him in spite of that and doesn't mind if it's directed at her now. She often gets jealous like the others if another girl is displaying any sort of affection or acting intimate with him. Still, whenever Issei says something that implies he is not a lolicon, she gets mad at him.

After Issei went into Juggernaut Drive (and after his return in Volume 12), Koneko has been having Senjutsu healing sessions with him in order to restore his life energy that was lost. During one session, she tells him that she would hate it if he died and that she would keep doing these sessions for the rest of her life if that was what it would take, making him promise to never use that form again. She offers a faster method to heal him, though it would involve them having sex, and a flustered Issei rejects the offer, as he wanted Koneko to be with someone she loves (as he still believed the girls around him didn't like him during this time).

Her love kept growing and growing until it reached its climax in Volume 11, where she went into mating season and chose him as her partner, but was stopped by her sister, Kuroka. Koneko soon after stops Kuroka's attempt to seduce Issei by declaring that he belongs to her. Later in the same volume, she proposed to Issei to be his bride, which Issei accepts under the condition that she grows bigger in both height and bust. She wants to be more than just a girlfriend to Issei because she chose him to be her soulmate. Her relationship with him is very serious, but will have to wait to develop more because her body is small and it would be dangerous for her to bear children at this point. When Issei died, she cried along with Ravel, but was also happy to hear his spirit was alive, embracing him when he returned. She is determined to marry him in the future, and will sometimes say that she will be Issei's bride one day. Koneko gave her first kiss to Issei after he protected her and Kuroka from the grim reapers and accepting her proposal in Volume 24.

In Volume 25, Koneko became much more bold towards Issei such as sleeping with him half-naked and wanting to reserve his child.

While celebrating at the Hyoudou residence, following the defeat of Vidar, the girls (Asia, Xenovia, Irina, Akeno, Kuroka, Koneko, Rossweisse, and Rias) tell Issei to show his love for them which he does and tells them that every one of them is his bride. This statement reveals that Issei is now planning to marry all eight of them.

In True Volume 2, she showcased her newfound boldness as she joined Akeno in dragging Issei into Akeno's lust room to spoil him before departing for their training camp, even to the point of being willing to have sex with him along with Akeno before they were interrupted by the other girls.

After witnessing her "Shirone Mode", Issei began having lecherous fantasies about her, waiting for her to mature to that height and bust size.

Yuuto Kiba
Kiba is the Knight of the Gremory group and best friend of Issei. In the beginning of the series, Issei is extremely jealous of Kiba due to him getting all the girls' attention with his good looks and had strong feelings of animosity towards him. Eventually, Issei started to think of Kiba as a good friend after spending time together with him whilst training and talking about their futures together. They both want to become strong so they can protect the girls of the Gremory group. Issei and Kiba have a good friendship and are willing to protect each other from harm. When Issei died, Kiba felt sadness and anger but kept it in. He released his anger on Siegfried, although losing but gained strength when one of Issei's Evil Pieces turned into Ascalon for him to use. Like the others, he gained hope when he found out Issei's spirit was alive.

Issei cares deeply for Kiba as his best friend and wants to grow stronger with him, with the both them making a promise become Ultimate-class Devils, with Yuuto being the Ultimate Knight and Issei being the Ultimate Pawn. Issei is very perceptive about his metal state and feelings as prior to facing Ewald Cristaldi, a legendary Excalibur wielder, Issei told him he can't die, showcasing his concern for him. When Issei was enraged by Rizevim and Qlippoth kidnapping his parents and attacking Ophis, Yuuto calmed him down by using the same words Issei used before Yuuto faced Ewald Cristaldi, as Issei thanked him and said it was good to have him.

Issei also worries about Yuuto due to not having a girlfriend despite his handsome looks and popularity with females, to the point of trying to get him together with Tsubaki Shinra, much to Yuuto's confusion. Issei feels that Yuuto is far too reckless at times and by having a girlfriend, he wouldn't be as reckless.

Yuuto also views Issei as a powerful rival and has several times stated he wants to be able to fight on his level or even defeat him. In True Volume 2, they finally get the chance to fight against each other in the Azazel Cup Rating Game between Rias and Issei.

Due to their deep friendship and fraternal relationship, some girls at Kuoh Academy have started to believe that they are in a secret relationship and the rumors of their relationship are so popular among the female student body that the Manga Club created a manga about it, a fact which annoys Issei.

Irina Shidou
Irina and Issei have been friends since childhood and reunited in Volume 3. Upon their reunion in, Issei and Irina's relationship became slightly strained due to being on opposing sides, as Issei challenged Irina to a duel after she and Xenovia, mocked Asia, in which Irina defeated Issei. They later agreed to work together to find the Excalibur fragments, in which Issei showed genuine care for Irina after finding her injured after her fight with Freed. It wasn't until after the Irina had reincarnated into an Angel and attend Kuoh Academy, that the two friends finally reconciled.

In Volume 9, she was incited to mate with Issei by Xenovia in order to help strengthen Heaven's forces, nearly turning into a Fallen Angel in the process after Issei accidentally landed his face on her breasts and groped them, causing her to have "impure thoughts". The next day, she was so embarrassed, that she blushes whenever she and Issei look at each other.

Issei was surprised to see her because as kids, he thought she was a boy. She had a crush on Issei since they were little, but was shocked to see that he has become a Devil and a pervert. Nonetheless, she kept her feelings for him. She wants to make love to Issei and have his children, like Xenovia, to apparently strengthen Heaven's forces out of influence of Xenovia's naivety. She loves Issei very much, but had trouble expressing it like the other girls because if she thinks or does something impure, she will become a Fallen Angel.

In Volume 16, it is revealed that Irina is working to find a way for her to make love with a devil without falling.

In Volume 18, it is revealed that Michael has crafted a special room that is located in a different dimension that would allow her to copulate with Issei without fear of falling, much to Irina's embarrassment. Irina and Issei spend some time together in the special room in which they reflect on their childhood and they become quite intimate before being interrupted by the other girls. Later on in the Volume, Issei states that no matter what, Irina is his childhood friend and is someone precious to him, much to Irina's happiness. At the end on the Volume, Irina kisses Issei in the snow. It is also revealed that she was Issei's first kiss when they were children.

In Volume 19, she started to become more bold in building her relationship with Issei, such as sneaking the doorknob that opens the special room in places he goes to, learning to cook for him, hugging onto him, sneaking into his bed at night, bathing with him and calling him "darling." She becomes slightly less concerned with falling in order to be with Issei, even offering to have sex with him.

In Volume 23, during the match, Irina made a proposal to Issei which he accepts. Happy with his response and becoming engaged to him, Irina gained a massive power boost using the holy aura of Hauteclere to send Angels flying left and right. Irina wishes to have two children with Issei: one boy and one girl.

In Volume 25, while celebrating at the Hyoudou residence, following the defeat of Vidar, the girls (Asia, Xenovia, Irina, Akeno, Kuroka, Koneko, Rossweisse, and Rias) tell Issei to show his love for them which he does and tells them that every one of them is his bride. This statement reveals that Issei is now planning to marry all eight of them.

Xenovia Quarta
Xenovia and Issei met in Volume 3 and did not care much for each other. Issei initially disliked her, as she called Asia a witch and wanted to kill her, but after the events of Volume 3, Xenovia apologized wholeheartedly and became a Devil after learning of God's death. She then decides that she wants to have strong children and chooses Issei to be her mate. She is completely oblivious to sexual situations due to her being raised in the Church and tries to have sex anywhere with Issei, even going so far as to bring condoms to school so they could "practice".

She wants his genes as the Red Dragon Emperor since she wishes to give birth to strong children as a way of making up time she feels she lost as a woman while in the service of God, rather than out of any romantic feelings she has for him. That changes after she begins to fall in love with Issei when he expressed his opinions to Michael to provide convenience for her and Asia to be able pray to God without experiencing the pain that came along with it. As the series progresses, it is shown that Xenovia has developed genuine romantic feelings for Issei due to his determination to protect his comrades even if he gets injured by doing so. She also emits a scary aura whenever the other girls are getting closer to him. Xenovia has displayed concerns that the path to being with Issei is becoming farther as other girls get closer, causing her to be more aggressive in seducing him, shown in Volume 16. Despite having difficulties understanding her personality, Issei is willing to protect her just as much as the other girls.

Like Asia, she also wants to join his peerage once he becomes a High-Class Devil, which happens in Volume 22 when she officially becomes his first Knight.

In Volume 19, Xenovia kisses Issei twice, once in Kyoto after making her wish and again in the Hyoudou household underground pool. After Xenovia kisses Issei for the second time, she thanks him for the lifestyle she is currently enjoying, which was only possible due to Issei, resulting in them getting closer.

In Volume 23, Xenovia made a proposal to have him take her as his bride, which Issei accepts. Happy with his response and getting engaged to him, Xenovia gained a massive power boost. During the match, Xenovia wishes to have five children with Issei: three boys and two girls.

In Volume 25, while celebrating at the Hyoudou residence, following the defeat of Vidar, the girls (Asia, Xenovia, Irina, Akeno, Kuroka, Koneko, Rossweisse, and Rias) tell Issei to show his love for them which he does and tells them that every one of them is his bride. This statement reveals that Issei is now planning to marry all eight of them.

Gasper Vladi
When Gasper and Issei first met, Issei thought that he was another girl and was shocked after learning that he was a cross-dressing boy. Issei often cursed him for being a shut-in, although Issei and Gasper became great friends and Issei trains him as his junior. Issei's blood gives Gasper a boost in power, even making him able to hit his Sacred Gear's Balance Breaker for a short time. After Issei apparently died in Volume 11, he seemed to transform in Volume 12, becoming filled with rage at the Khaos Brigade for killing his friend and senpai, and proceeded to defeat Georg with his new power.

The two of them are a proper senpai-kouhai, and Issei has taught Gasper several things and also helps Gasper with his troubles. The two are on extremely good terms and are a strong team. Issei appears to also teach much of his perverted ideals to Gasper, which the latter seems to be innocent enough to admire. Twice, Gasper has even helped Issei to use his Dress Break by freezing their targets in place beforehand with his Sacred Gear.

In Volume 16, Issei swore to help Gasper rescue him childhood friend, Valerie Tepes and was proud of his growth as Gasper showcased his bravery and courage.

Rossweisse
Rossweisse is the second Rook of Rias' peerage and a teacher at their school. Issei and Rossweisse have a student-teacher relationship, where Rossweisse is shown to be giving advice to Issei on various stuff from Issei's studies in school, training, and even his relationships with the girls. Rossweisse later gained some interest in Issei during Volume 12, where she and the Occult Research Club members all asked Issei out on a date.

In Volume 17, she asks Issei to become her boyfriend due to her grandmother coming to visit, to whom she told that she does have a boyfriend when she actually doesn't. Later on in the volume, they go out on a date to Tokyo which was interrupted by the appearance of Euclid Lucifuge. During the attack on Auros and Agreas, Issei rescues Rossweisse from Euclid, defeating him in the process. By the end of the volume, Rossweisse develops feelings for Issei, even asking him out on a date to a 200 yen shop next time. In Volume 22, under Rias' orders, Rossweisse was transferred to Issei's peerage, becoming his first official Rook.

In Volume 25, Hyoudou Residence, Issei returns to sleep only to find Rossweisse on his bed wearing a revealing lingerie and shyly asked if he’s gonna come to the bed and then Issei went to his bed and laid down. Issei was shocked about Rossweisse attempts to offer her virginity in order to break off her engagement and reveals to Issei that she doesn’t want to marry Vidar and wants to be on Issei’s side, asking him to snatch her away from the Norse chief-god. Issei reveals that he has no intention to give Rossweisse to Vidar and recalling on how he did with Euclid, hugging her telling her to believe in him. Realizing that their face was too close to each other Issei and Rossweisse backed away with their faces turning red but Rossweisse came close to Issei and gave her first kiss, much to Issei’s surprise. Kuroka and Koneko then barged into the room and started seducing Issei. Wanting to keep Issei to herself for the night, she tells them that she will be sleeping with Issei. In the end, Rossweisse and the Nekomata sisters slept with Issei for the night.

During the match against Vidar, Rossweisse tearfully accepted Issei's proposal and promised to give birth to many of Issei's children, making her his eighth bride. After she defeats Brynhildr and Issei defeats Vidar, Rossweisse blushingly promised to show Issei the real World Tree Yggdrasil, implying she wanted to go on another date with him. At the party after the match Rosseweisse, (once again in a drunken state), clings to Issei's back declaring that he is her husband and refuses to hand him over to the other girls.

While celebrating at the Hyoudou residence, following the defeat of Vidar, the girls (Asia, Xenovia, Irina, Akeno, Kuroka, Koneko, Rossweisse, and Rias) tell Issei to show his love for them which he does and tells them that every one of them is his bride. This statement reveals that Issei is now planning to marry all eight of them.

Ravel Phenex
Ravel and Issei met during the Rating Game between Rias and her brother, Riser, and didn't really care for each other. After he defeated Riser at the engagement party, she became infatuated with Issei and starts to develop feelings for Issei, albeit in a tsundere fashion.

In Volume 10, she moves in with him and transfers to his school in order to spend more time with him. She has stated that she does not mind becoming one of his concubines as long as she is by his side. Issei, however, remains oblivious to her feelings but was still willing to put his life on the line to protect her under Lady Phenex's request to take care of her. It is implied in Volume 9 that Ravel enrolls in Kuoh Academy so she can get closer to Issei, and moves in with him in the following volume. She happily accepts Sirzechs's request of becoming Issei's manager and continually works hard for him, such as finding a suitable magician for him to make a pact with.

Issei respects and admires her a lot for the knowledge and dedication she puts in her work as a manager and completely trusts in her judgement. He has stated that he would like to have her as his manager forever and maybe as a tactician in his peerage when he becomes a High-Class Devil with his own Evil Pieces. Issei officially becomes a High Class Devil in Volume 22, when Ravel officially became his Bishop, along with Asia.

In Volume 23, Ravel became more bold after becoming a member of Issei's peerage, such as shyly expressing her desire to sleep with him while Rias and Akeno aren't around and wearing a transparent white negligee. She's more determined as she allows him to touch and squeeze her breast and fights with Church Trio for his affections and who gets to sleep with him. After the Rating Game against Dulio, Issei comforted her when she was crying due to feeling that she couldn't help Issei win.

Ingvild Leviathan
Issei first meets Ingvild at the park, where the fountain was and she immediately recognized him as the Red Dragon Emperor. When Issei defeated the mysterious devils, he used his handkerchief to wipe off the blood from her face. When they meet again, Ingvild started to sing, which causes pain to his body but he holds off Yuuto and Xenovia from attacking her because he knows she meant no harm. When Ingvild woke up from her sleep, Issei took her to the beach and they started to become closer and eventually befriended each other, he was about to invite her to eat until they were interrupted by Nyx. Ingvild was contacted by Issei through Akeno’s breasts to ask her to sing for him, she was hesitant at first due to the pain she could inflict on him, but agrees to his request to sing for him, which empowered Issei. After Nyx was defeated, Ingvild eventually became his first servant to join his peerage as his Queen, as he agrees to let her sing under his leadership.

In True Volume 2, Ingvild was among first group of brides in Issei’s dream that’s will marry him, hinting Ingvild will become one of Issei’s future brides. When Akeno and Koneko were seducing him in Akeno’s erotic room, Ingvild innocently thought of hugging Issei with her naked body but was embarrassed to do so, concerning Issei when he believed the other girls were starting to affect Ingvild.

In True Volume 3, Nimura suspects that Ingvild is also attracted to and in love with Issei too.

Sona Sitri
Sona at first treated Issei like a regular servant, but as time went on, she grew to admire him for his tenacity and courage. She respects him greatly for everything he has done, but she is also jealous as well because Issei solved many of Rias' problems for her which she, as her best friend, could not do anything about due to her position as a High-Class Devil. She considers him as a friend as he is Rias' boyfriend and suggested to Issei that he should call her by her first name, and told him to take care of Rias even though she's stubborn and has a great deal of pride. She has admiration and respect for him and for his accomplishments and everything he has done for Rias, and she also congratulated him on his promotion recommendation to Middle-Class Devil.

Tsubaki Shinra
Sona's Queen, of whom Issei is aware of her feelings for Yuuto Kiba and often encourages her to try her best to get his attention (mostly worried that Kiba might be interested in him instead). Issei and Tsubaki also exchange emails regarding Kiba, much to his confusion. Like Sona, Tsubaki has also praised Issei for achievements.

Genshirou Saji
Saji and Issei have a friendly rivalry going on because they are both Pawns, they both harbor feelings for their masters, and they both have Dragons sealed inside their Sacred Gears. At first they did not care for one another, but as time progresses, they eventually became good friends, even stating that they are "War Buddies" in Volume 3 of the light novels and have started training to become strong to face one another again. When Issei died, Saji showed expressions of anger and sadness due to him being killed and wanted to avenge Issei. Saji is quite jealous of Issei and his relationship with Rias, because Saji has not made any progress with Sona, he is even more enraged at how close Sona and Issei had become.

Despite being good friends with one another, Saji is very envious and jealous of Issei, even to the point of seemingly developing an inferiority complex towards him. While Issei has made tremendous growth in strength and has made his master his girlfriend, Saji has felt left behind in comparison. He is also jealous of how close Issei and Sona have become, lamenting his own lack of progress with Sona. He laments the fact that he will never surpass Issei in power, no matter how hard he tries. It is not until he states his dream and finally obtains his Balance Breaker that he stops comparing himself to Issei. When the two of them fight once again in the Azazel Cup, Saji is able to put up a good fight against Issei but is ultimately outmatched and defeated.

Bennia
Issei first met Bennia in Volume 14, as she begged Sona to bring her along to Issei's home since she is a huge fan of his, being an Oppai Dragon enthusiast and having a large collection of the Oppai Dragon goods which she puts on the back of her robes.

Tsubasa Yura
Issei and Tsubasa get along well since both are well fitted for physical work. In the short story "The Student Council’s Decision", when Issei temporally replaced Saji after the latter had caught the "Dragon Flu", he initially worked with Tsubasa who guided and lead Issei on the Student Council work such as inspection of school clubs activities. During lunch break, Tsubasa admitted to Issei that she likes him more compared to all the other boys they know.

She congratulated Issei for his promotion recommendation to Middle-Class Devil and asked for his autograph, saying that Issei is the type of guy that she likes because he is always muddy after a fight, and admired Issei for his fight with Sairaorg Bael. She has a crush on Issei.

Tomoe Meguri
When Issei was temporally filling in for Saji's Student Council work, he was partnered with Tsubasa and Meguri to assist him, they generally maintain a mutual friendly relationship.

Reya Kusaka
When Issei substituting for Saji in the Student Council, the two have shown be close as during their lunch break, they discuss exchanged personal deeds about the members of their respected club members such as who likes whom and how members of the Student Council see him. Furthermore, she called him a pervert in a playful tone rather than the usual insult.

Momo Hanakai
Not much is known about Issei and Momo's relationship, aside from their first interaction during their Masters Rating Game, Momo felt disgusted over how perverted he was when he used his Pailingual on her and the other girls present. But they appear to be on friendly terms in general, as when it appeared how Issei was becoming close friends with Sona, Momo cheered him on to get Sona to fall for him so she could date Saji.

Ruruko Nimura
Not much is known about Issei and Ruruko's relationship, but like Momo, Ruruko gives him support to get Sona to fall in love with him so she could also date Saji.

Raynare
Raynare was Issei's first girlfriend, who disguised herself as Yuuma Amano to trick and deceive Issei in order to kill him because he was deemed as a "threat". She killed Issei with a light spear at the end of their date, and afterwards killed Asia by stealing her Sacred Gear, Twilight Healing. This caused Issei to hate Fallen Angels altogether. Issei later defeats Raynare and she again tried to deceive him (due to her becoming Yuuma once more) when she was trying to convince him to spare her life, but he sees through her ruse and asks Rias to kill her.

Although dead, Raynare left a permanent mark in Issei's heart, as explained in Volume 10 when Koneko, Asia, and Akeno try to "heal" Issei. She made Issei fear women after he planned his whole first date with Raynare, only to be killed and treated terribly by her. She also made him afraid to call girls by their first name (i.e. calling Rias "President (Buchou)" instead of her name), and also made him afraid of being disliked by other girls or rejected if he ever showed his feelings again. After being laughed at by Raynare in their final confrontation, Issei also seemed to form a sort of mental block, making him oblivious to the feelings of the women around him. For example, before Volume 10, he constantly assumed that Akeno and Rias's attention is because he is a 'cute kouhai' and something like a pet to them. The girls, however, eventually figure this out and Raynare's "curse" is lifted from Issei's heart. After this, he is noticeably more perceptive of the girls feelings, though he is still oblivious at times.

Azazel
Issei, at first, hated Azazel because he was a Fallen Angel, but learned later on that he means well and has good intentions. Issei respects Azazel a lot, even calling him "Sensei" after Azazel tells him that he would teach Issei the secrets of the Sacred Gear and how to ensnare beautiful women. Azazel later became the Occult Research Club's advisor in Volume 4, and aided the Gremory team on how to better improve themselves as a team. He also helped out in progressing Issei and Kiba's Sacred Gears, as well as helped Issei learn how to achieve Balance Breaker and control the Triaina. He also shows a great deal of concern for Issei, as shown after Issei's death, but was relieved to hear his spirit was alive. They seem to be very close to each other as they are usually seen discussing various matters regarding the mythical events and the people around him. Issei is very close to Azazel to the point that in Volume 22, he is a bit saddened knowing the fact that Azazel is not present to his High Class Devil promotion and wanting Azazel to see his achievements, because of his great sacrifice of fighting Trihexa at the Isolation Barrier Field.

Baraqiel
Baraqiel at first hated Issei because he misunderstood the meaning of Oppai Dragon as a Dragon who feeds on breasts, instead of a Dragon who loves them and believed that Issei wanted to eat the breasts of his estranged daughter, Akeno. However, since coming to understand the mistake and having been reconciled with his daughter because of Issei and Akeno's feelings for him, Baraqiel has shown his approval and respect for him.

Michael
Issei sees Michael as a very powerful leader and respects him very much. Likewise, Michael has also shown to have a great liking towards Issei. In Volume 4, Michael gave Issei Ascalon as a symbol of peace between the Three Factions prior to the events of the Kuoh Treaty. Also, Michael agreed on Issei's request of allowing Asia and Xenovia to pray without receiving damage as a devil. Later on, he, along with some of the angel researchers, developed a room to allow angels to procreate more easily in support of Issei and Irina's relationship.

Gabriel
There is not much to say about their relationship, other than the fact that even in their first meeting, Issei always thought lecherous thoughts of her, but at the same time, acknowledged her position as one of the Seraphs and her beauty as the most beautiful woman in Heaven. In Volume 18, She came to greet Michael and the Gremory team while also wearing a Santa costume. While Issei was thinking lewd thoughts of Gabriel, she hit his forehead in an adorable way. Gabriel returned to Heaven from a business trip in the Human world after hearing about the attack in Heaven. She was unaware that her breast was seen by Issei due to him using his newest ability "Penetrate".

Dulio Gesualdo
They seem to have a friendly relationship and respect one another. Dulio sees him as a brave Oppai Dragon hero, like Issei sees and respects Dulio as a suited powerful leader of the D×D. Before their match in the Azazel Cup, Dulio playfully told Issei that Mirana has a large bust which will useful to him. During the match, Issei and Dulio displayed a friendly rivalry, as they wished to defeat each other.

Griselda Quarta
They have seen to have a friendly relationship with each other, as it is seen when she entrusted Xenovia in Issei`s care, claiming that she will live a happy life with him and her friends.

Sirzechs Lucifer
Sirzechs is Rias' older brother and met Issei during his duel against Riser at Riser's and Rias's engagement party. He shows a great interest in Issei and considers him part of his family, even asking Issei to call him his big brother, though Issei considers it impossible to call a Satan brother. He showed anger at Issei's death and, like the others, wanted to avenge him. He was also happy to hear that his spirit was still alive. He has shown great faith in Issei's relationship with Rias as they progressed on. He later passed on his role of "taking pictures of Rias while she was sleeping" to Issei, though Rias was upset and said she didn't mind Issei doing it but heavily rejected Sirzechs with doing such things. Issei was greatly saddened when Sirzechs departed to the Isolation Barrier Field, as he wanted to spend more time with him and do many things with him.

Serafall Leviathan
She has a minor rivalry between Issei's show Oppai Dragon and her own magical girl television series, but is shown to get along well with Issei.

Ajuka Beelzebub
Ajuka appears to like Issei, even being willing to correct the overwritten code of his Evil Pieces because of the Juggernaut Drive to prevent malfunctions and along with this intentionally approving of cheat-like abilities in Rating Games. Whether this is more of an experiment on his part, a favor to Sirzechs or for some other reason is still unknown.

Falbium Asmodeus
Falbium is the laziest among the four Satans to the point that he leaves everything to his servants much to Issei's dismay but he still helped in administering a trial for Issei and Rias in Volume 8 dressing as Satan Green.

Zeoticus Gremory
Zeoticus Gremory is Rias' father and meets Issei through her (although after the fight with Riser). He at first was disappointed at the fact Rias did not marry Riser to connect the families, but later accepted his daughter's content of loving Issei. He became fond of Issei and becomes good friends with Issei's parents and accepted him happily into his family, even wanting Issei to call him father. Like Sirzechs, he also shows great faith in Rias and Issei's relationship, although he often embarrasses the two (more often Rias).

Venelana Gremory
Venelana is the mother of Rias. She, like her husband, was also very disappointed at the fact that the engagement between Riser and Rias broke off. She, however, decides to accept her daughter's decision to love Issei and became fond of him. She is willing to accept him as a member of the Gremory family, even wishing for him to call her Haha-ue (respectable way of saying mother) or Okaa-sama (mother). She teaches Issei how to dance and eat elegantly and become a proper gentleman so that he does not embarrass Rias at social events in the Underworld.

Issei tends to have lewd thoughts about her as she has great resemblance to Rias.

Grayfia Lucifuge
Grayfia is the wife of Sirzechs and Rias' sister-in-law. She first met Issei while retrieving Rias, who was in the middle of trying to make love with him. She was there after the Occult Research Club's defeat in the Rating Game against Riser, and helped Issei bring Rias back and stop the engagement. She shows great concern for Rias but accepts Issei as her lover. Like the rest of the family, she is also fond of Issei. In Volume 12, she was one of the few to not even consider the possibility of his death, stating that she 'would not allow the person who will become her brother-in-law to perish with something like Samael's curse'. At the onsen in Izu, it is revealed that she is very happy about Issei joining the family and treats him as her little brother and washes his back, much to his surprise. She also demands to be called "Ane" (elder sister) by Issei— much like how Sirzechs wishes to be called "Onii" (elder brother).

He greatly respects her and looks up to her while at the same time being a bit intimidated by her due to her strict nature. When her biological brother Euclid started resurfaced as a member of Qlippoth, Issei swore to defeat him and drag him to Grayfia in order to clear her name.

Millicas Gremory
Like his father, Millicas likes and respects Issei calling him "Issei nii-sama". In fact, when Sirzechs asks Millicas whether he likes Oppai Dragon or Satan Red more, Millicas chose Oppai Dragon much to the shock of his father. They have a brotherly bond, he even asks Issei to call him by his name without honorifics due to feeling lonely about Issei calling Rias by her name which made him very happy when Issei did. When Grayfia started to become a member of Issei’s team in order to make her leader a Satan, Issei showed his care for Millicas by telling Grayfia to spend more time with her son because he is lonely and needs a parental figure.

Lady Phenex
She is the mother of Ruval, Ravel, and Riser. She met Issei in Volume 10, Issei initially thought that she would hold a grudge against him for his action of destroying the engagement ceremony, but to Issei's fortune there are people with big hearts in the house of Phenex. Lady Phenex asked him to take care of Ravel so no weird pests (boys) would come near her, knowing full well that Ravel is in love with Issei and was willing to only be of use to him and be one of his concubines.

Riser Phenex
Issei initially disliked Riser because he tried stealing Rias away from the group, which Issei did not want. At the end of the Rating Game between Riser and Rias' peerages to determine whether Rias should wed Riser, Issei went against Riser but ran out of stamina and was beaten to near-death before being saved by Rias, who surrendered in order to prevent any further harm to him. He woke up two days later and went after her, interrupting the engagement party, and Sirzechs decided on a one-on-one battle. During that fight, Issei gave up his left arm to reach his Balance Breaker for a very limited amount of time consisting of ten seconds and ended up defeating Riser with a strategy/fallback plan that should his armor disappear before he defeated Riser. Issei made him go into a state of depression due to the fact that he has never lost and also made him afraid of Dragons. Issei didn't really hate Riser after he took back Rias, as shown when he agreed to help him get back on his feet under Ravels request, at that time the two developed a friendly rivalry and even talk with each other via magic circle, but Riser is still jealous of Issei's relationship with Rias and wants to fight him again. Later on during the invasion of the Underworld, after he overcame his fear of Dragons during Tannin's training which was organized by Issei and Ravel, he went out fighting in an attempt to counteract the monsters and also tried to help Ravel deal with Issei's death.

Isabela
One of Riser's Rooks, after Issei defeated her in the Rating Game between their masters with Dress Break and Dragon Shot, Isabela started to respect Issei's strength, even stating that if he becomes even stronger she'll be able to boast about her story as well. The two of them seem to have developed a small rivalry with each other.

Mira
One of Riser's Pawns, she initially disliked Issei for being a pervert and using Dress Break on her during their masters Rating Game. She easily beat up Issei in their first encounter, but Issei later returned the favor during their masters' Rating Game. However in DX.1, she apparently becomes a fan of his, even asks for his autograph.

Sairaorg Bael
Sairaorg is the cousin of Rias who met Issei when they were deciding Rating Game matches between the young Devils. He is known as the strongest young Devil. Wanting to fight each other from the beginning, they then sparred before their match, in which Issei found him to be extremely powerful and Sairaorg finding Issei to be interesting. Issei held incredible respect and admiration for Sairaorg for his strength and relentless determination, addressing Sairaorg with the honorific-san.

During the Rating Game match between Rias and Sairaorg's peerages, Issei and Sairaorg went head-to-head in a fist-fight match. Later, Issei found that Regulus, his Pawn, was a Sacred Gear which he combined with and activated his Balance Breaker. The fight continued and ended with Sairaorg being knocked out while still standing. After the match, the two became close friends and promised to get stronger to fight each other once again later on. When Issei apparently died, he came and encouraged Rias to get up from her depression. He believed that he was not dead due to the fact that he had not had sex with the woman he loves. He was happy when Issei returned from his presumed death and impressed that he did so with Great Red's help.

Lord Bael
Despite having never personally met each other, according to Zekram, Sairaorg's father holds a strong hatred towards Issei, as Lord Bael is very jealous of Issei's power, fame and achievements as the strongest young Devil, despite being a reincarnated Devil; a fact which strongly opposes his personal viewpoint of Devil blood purity.

Zekram Bael
Unlike Lord Bael, Zekram doesn't seem to hate Issei despite him being a reincarnated Devil. While he still maintains his view on the old pure-blood devil traditions, he acknowledges Issei's power and achievements, even asking him if he has a interest in becoming a Satan, stating that with his achievements and popularity, it would be interesting if he became a Satan. He is shown to have accepted the relationship between Rias, who is a pure-blooded devil princess and Issei, despite him being a reincarnated devil, though he states that Issei must promote to High-class Devil to be fully accepted, telling Issei that when he promotes, he will invite him and Rias to his castle and serve them cake made from apple grown in the Bael territory. After the defeat of the Alliance of Hell, Zekram gave his approval to Ajuka Beelzebub in regards to promoting both Issei and Vali Lucifer to the newly created Special-class and acknowledging them as Super Devils. Zekram has also shown approval about promoting Issei to a Satan, stating that even if he loses in the Azazel Cup, it wouldn't affect his candidacy as a Satan.

Diodora Astaroth
Issei hated Diodora from the start as he was trying to take Asia away. Diodora, in turn, looked down on Issei, referring him as a "filthy Dragon" and stated that being touched by him made him feel sick. Issei's hatred for Diodora grew to its peak when he learned that the noble set up Asia on purpose on the day she healed him, which resulted in her excommunication from the Church and labeled as a heretic, just so he could add her to his "collection'. Issei later easily overpowered Diodora during their final confrontation, much to latter's rage. After being beaten by Issei, Diodora developed a short-lived fear of dragons.

Diehauser Belial
Issei at first admired and respected Belial as he was at the top of the rating games. At Volume 20, he was saddened when he learned that Diehauser was in fact a traitor, and tried desperately to stop him from revealing the corruption of the rating games as it would cause chaos and unrest. When Diehauser revealed his true intentions, Issei regained his respect for him.

Seekvaira Agares
At first the two of them have a vague relationship, as Issei tries to avoid her as much as possible because of her cold and strict nature. They later meet up, and the two of them start to get along, knowing the fact that both of them are Otaku fans. She later gained an interest in Issei through their similar comparability in Otaku mecha, shorty there after they are on friendly terms.

Roygun Belphegor
They first meet at the Gremory training area in Volume 23, where Roygun has become Issei's advisor for the Azazel Cup. She took a interest in Issei, flirting with him and calling him "cute", which causes Issei to become embarrassed. Roygun then asks if Issei doesn't like older women as she's over a century years old, to which Issei responds that he sees her a beautiful Onee-san in her early twenties, much to Roygun’s happiness, and this causes Asia, Xenovia, Irina, Rossweisse and Ravel to become jealous. Roygun finds Issei’s words to comforting and is happy that he complimented her. After this, she tells Issei that she will be watching his match against Dulio. After the match, she reappeared before Issei again and joins his team, while at the same time, pledging her and her peerage's service under him and exchange she will dedicate all of herself to him. In Volume 24, they seem to have to become close as Roygun was willing to assist Issei with guarding the Azazel Cup against any threats, for which Issei was grateful.

In True Volume 2, Roygun becomes one of Issei’s brides attending the wedding ceremony in the vision Chichigami made Issei, hinting that Roygun will fall in love with Issei and become one of his future brides. During the Rating Game, Issei express his concern for Roygun when she went to fight her opponents alone in a injured state and wanted to assist her, but was stopped by Ravel.

After learning that she will be a temporary nurse of Kuoh Academy, he was thinking of hurting himself to visit her in the infirmary and was tempted when she said that she can cure his virginity.

Roygun shown to desire to become his lover, as she needs to find a husband after being disowned by the Belphegor Clan.

Vali Lucifer
Vali is Issei's rival and the holder of the Longinus, Divine Dividing. When they first met, Vali was on another level compared to Issei, which made Issei devoted to becoming more powerful. During the signing of the peace treaty between the three factions, he went against everyone and formed a team in the Khaos Brigade. This made Issei hate him and after which they fought with Issei in Balance Breaker mode due to Azazel's bracelet. Issei won the fight due to Vali teleporting away.

In Volume 6, Vali approached Issei to congratulate him for attaining his completed Scale Mail Balance Breaker and to warn him about Diodora Astaroth. Later during the volume, after Issei goes berzerk due to Juggernaut Drive, Vali helps the Occult Research Club revert him back, thus saving his life. After that, the two of them witnessed Great Red emerging from the Dimensional Gap as the two of them promised to fight each other as the two fist bumped each other, with Vali claiming that Issei is amusing and asked Issei to become stronger.

During Volume 7, Vali appeared to save Issei after he was bitten by Fenrir. After Issei woke up, Vali stated that while he cannot defeat Loki and Fenrir alone, it would be a different story if the Two Heavenly Dragons join forces, stating he didn't mind fighting alongside Issei. As Issei wondered why Loki hates peace, Vali stated that there are people who consider the so-called peace painful (a phrase that had a deep impact on Issei and stuck with him as he pondered about it during various times). Vali reveals while he was initially disappointed that Issei was a Red Dragon Emperor who was talentless and weak, but he praised Issei for trying to master Ddraig's power by communicating with him as Vali stated that he would like to have a match similar to a Rating Game between his own team and a team that Issei creates.

In Volume 9, Vali sent Le Fay Pendragon along with Gogmagog to assist Issei by foiling the Hero Faction's ambush. After receiving Le Fay's report, Vali noted that Issei has begun to make contact with the past possessors of his Longinus and that Vali is doing the same, though Vali stated that unlike Issei, who is trying to convince the past possessors by words, Vali would take the greater challenge of dominating the past possessors as he claimed that it was more fun that way. Vali stated that Cao Cao should defeat them while he still has a chance and before the Two Heavenly Dragons completely surpass his powers.

In Volume 10, Vali sent a message to Azazel, claiming he would protect the Issei's match against Sairaorg as he was looking forward to it.

In Volume 11, Vali sent Ophis to Issei's place as she was interested in Issei's growth and also to protect her against Cao Cao and the Hero Faction. After being defeated by Cao Cao and poisoned by Samael, Issei later visited Vali and talked to him about Cao Cao and Ophis as both reaffirmed their promise to fight each other and promised to survive the upcoming fight. As Issei stayed behind in the collapsing subspace to defeat Shalba Beelzebub and save Ophis, Issei promised to defeat Shalba on Vali's behalf too, causing Vali to smile.

In Volume 12, in a conversation with Yuuto Kiba, Vali promised to avenge Issei. After Issei returned from the dead, Vali was there to greet him and showed Issei his Empireo Juggernaut Overdrive, which he used to defeat Pluto. After Issei defeat Cao Cao and Cao Cao told him that Vali's rival is the best, Vali stated that he won't hand over his rival to anyone and stated that the only one who has the right to defeat Issei is him. After learning that Issei came back to life with the flesh and power of Great Red, Vali told Issei that he has to finish his battle with Issei first before challenging Great Red as Vali warned Issei that many people will come for his life due to his contact with Great Red and Ophis.

In Volume 16, Vali and Issei teamed up against Crom Cruach as Vali wanted to confront Rizevim Livan Lucifer while Issei wanted to save Gasper's childhood friend Valerie Tepes. Despite their combined assault, the two of them were unable to defeat Crom Cruach, as he simply stalled them for 10 minutes. Vali and Issei later joined Team DxD together, becoming the vanguards against Rizevim.

In Volume 17, Vali and Issei trained together with Sun Wukong, as the two complimented each other's special forms, as Vali stated that Albion and Ddraig are having difficulty drawing answers about Issei and Vali's new powers due to the past White Dragon Emperor's hate towards Ddraig and Issei.

In Volume 20, Vali and Issei teamed up to fight Rizevim and Diehauser Belial. While Vali was initially irritated due to him not wanting Issei to interfere his fight with Rizevim, he softened his tone after seeing Issei's parents captured by Rizevim and told Issei that he has to survive since he promised to rescue his parents. After Vali was overwhelmed by Rizevim, Vali watched Issei fiercely fight for his family. After Issei attained Diabolos Dragon and defeated Rizevim, Vali complimented him, saying that he was captivated watching Issei fight for his family.

In Volume 21, Vali came to see Issei when he was recuperating in the hospital where he meet Issei's parents. While conversing with them, Vali told them how he initially wanted to kill them to make Issei an avenger, asking if they forgive him becoming happy when they did. Vali later teased Issei by mentioning to his parents that Issei got angrier when Vali threatened to halve Rias' breasts more then when Vali threatened to kill Issei's parent, as he laughed in amusement when Issei got scolded by his parents. While coming over to discuss the plans for 666, Vali restated his desire to fight a team created by Issei not just his peerage, as he stated that compared to fighting the Rias' peerage, he would prefer to fight the team his rival created more. The two of them promised each other to survive and overcome the oncoming fight. After defeating Aži Dahaka and Apophis, Issei and Vali talked to each other in the medical room about Issei's Dragon Deification and the fact that Azazel sealed himself in the Isolation Barrier Field. The two of them promised to see Azazel again, at least to complain to him one more time.

In Volume 22, Vali along with his team went finishing with Issei and the Occult Research Club, as the two of them discussed Issei's journey and his upcoming High-class Devil promotion as Vali revealed that he was already promted to Ultimate-class Devil as Vali revealed that he was excited for the Azazel Cup as he wished to see Issei participate as well. Later, Vali and his team attended Issei's High-class Devil promotion. Vali later greet Issei when he arrived at the venue with his team, as Issei stated the he wishes to have a good match against him as fellow Heavenly Dragons.

In Volume 23, Issei, Vali and Saji went fishing as the three of them discussed finding enjoyment in a fight as well as the upcoming fight between Sairaorg Bael and Cao Cao as well as the fight between Issei's team and Sona's team and later went to see Rias' Rating Game which revealed that Crom Cruach was her Pawn as Issei and Vali reffirmed their promise to meet each other in the finals.

In Volume 24, Issei protected the Rating Game between Vali and Rias from the attack of Thanatos and his Grim Reapers, as he stated that was looking forward to it more then anyone.

In Volume 25, during the party, Issei stated that if he and Vali get matched up together, there won't be any stage like theirs as Vali revealed that he wanted to continue the fight that they had during the peace meeting of the Three Factions.

Later into the series, the two of them have started to become friends; although they are still in a heated rivalry. They even promised to fight each other someday and continue to grow stronger until then.

Issei and Vali share a few similarities they are both powerful Heavenly Dragons, with degrading nicknames, they both have comrades who they care deeply for, they both have deep relationship with Azazel. However, at the same time they are different in other cases such as; Vali enjoys the idea of fighting strong opponents and finds the idea of peace boring, while Issei openly welcomes it. Vali is also shown to be calm and collected, while Issei tends to be reckless and easily angered. These similarities and differences are enough to establish Vali as a foil to Issei.

Kuroka
Kuroka is the elder sister of Koneko. She met Issei in Volume 5 when she tried to take Koneko, with Issei and Rias stopping her. He fought her for Koneko, and almost punched her in the face, but stopped at the last moment and warned her that if she ever tried anything again, his fist wouldn't stop. During Koneko's mating season, she made matters a little worse by stimulating Koneko and Issei. Although she stopped her sister, she still began to seduce Issei because she wants his "genes" for strong babies, which she tried with Vali but he denied, though it was stopped by Koneko. Issei later learns more about her past while she is receiving healing and tells Koneko that she is a good person, although she remains a "naughty cat". She has an attraction towards Issei and later develops strong romantic feelings for him.

She reappears in Volume 7, claiming Issei became more manly and asks him to have children with her because she is interested in strong genes and the holders of the Sacred Gears of the Heavenly Dragons would potentially make powerful offspring, but Koneko refuses to give Issei to her. The reason why she proposed Issei her offer was because she was initially refused by Vali.

In Volume 11, when Koneko enters mating season, Kuroka attempts to seduce Issei after she managed to revert Koneko back to normal. Although this attempt is interrupted by an exhausted Koneko, declaring that Issei is hers. Kuroka leaves and quietly tells Issei to look after her sister, showing how much she cares for her sister and how much she trusts him. While recovering due to her injuries from Cao Cao, she explains to Issei the reason why she killed her master. Issei later lessens his hostility towards her, claiming she's clumsier than he is. Unamused by the conversation, she claims that she doesn't want to hear that from him, but she thanked him as he leaves, though she pretends to be asleep.

In Volume 14, during her stay at the Hyoudou Residence, they became friendlier as Issei was willing to help the two sisters reconcile their relationship when the time comes, adding that Koneko's smile was the most important thing to him. Kuroka finally understood the reason why all the girls around Issei were falling for him, claiming that he was more charming than normal handsome men, indicating that she has developed romantic feelings for Issei as well.

In Volume 15, she became slightly closer to Issei, hugging him while rubbing her cheeks against his, telling him that he shouldn't become like the Evil Dragons and remain being the Oppai Dragon, while sitting on his lap. It is also revealed by Issei that ever since she has been staying with him, she has been getting closer to him more often.

In Volume 24, their relationship becomes even closer than ever upon learning the full truth about the Nekomata sisters upbringing, they had a heartfelt moment where Kuroka admitted to him she kept the hard truth hidden from her sister to protect her. Kuroka then hugged Issei pleading to continue living peacefully with him and her sister, promising to make amends for any trouble she's caused them and fight off any threats in the future, Issei hugged her back assuring that he will protect her and Koneko, thus establishing each other as family now. Through their communication, Kuroka revealed that she fell in love with Issei because he was kind to her sister Koneko and gave her and Kuroka a place to live and seeing him smile made her heart filled with love. Kuroka then confess her love for Issei which he reciprocates and wishes to have children with him. After the confession, Kuroka begins to call Issei by his name and kisses him for the first time.

In Volume 25, Kuroka became much more seductive and affectionate towards Issei after the proposal, such as wanting to have many children with him, nibbling his ear and sleeping with him. Kuroka said to Rossweisse while rubbing her belly that in the near future, she will have Issei’s child.

While celebrating at the Hyoudou residence, following the defeat of Vidar, the girls (Asia, Xenovia, Irina, Akeno, Kuroka, Koneko, Rossweisse, and Rias) tell Issei to show his love for them which he does and tells them that every one of them is his bride. This statement reveals that Issei is now planning to marry all eight of them.

Le Fay Pendragon
Le Fay is the witch of the Vali Team whom Issei meets in Volume 9, where it is revealed that she is a huge fan of his show, Breast Dragon Emperor Oppai Dragon (Oppai Dragon for short), wanting to shake hands with Issei and asked for an autograph upon meeting him. She later gives him advice on boosting his magic power as well as choosing a magician to form a contract with. She herself was considered a perfect candidate to be that magician by Ravel's statistics, but unfortunately Ravel refused to let her take up that position, because of Le Fay's status as a terrorist of the Vali Team rendered it impossible for her to become publicly associated with Issei. However, Le Fay was able to become Issei's contracted magician, because it was revealed in Volume 16 that because the Vali Team had been pardoned of their crimes and that Arthur had requested Issei to take her as his contracted magician for the reason of protecting her. Issei accepted his request, and asked Ravel, who agreed since she said that since the group has been pardoned of their crimes, Le Fay has become a legitimate magician to hire. Le Fay appears to have some affections towards Issei, expressing desire to go a shopping date with him. She also quietly expressed jealousy while watching Issei's brides fight over him.

Arthur Pendragon
Arthur seems to have deep trust towards Issei by leaving his dear sister, Le Fay, in his care, believing that he is able to protect her and have her return home to her everyday life by having her as his contracted magician. Issei accepted his request and Arthur intends on repaying him for it.

Tobio Ikuse
They first meet each other in Volume 15, alongside Dulio and sister Griselda. There he and Dulio help Issei and Saji have a sparring and train briefly the two dragon possessors, they seen getting along to each other and have a friendly relationship as he usially helps Issei and the Gremory group from behind the scenes during the sudden attack of Walburga. They also make a friendly chat about Vali’s history and his arrogance in childhood.

In Volume 24, Issei and Tobio became friendlier as they work together to defend Rias’s and Vali’s match. Issei at first was worried about Tobio and his team joining him because they are the important agents of the Grigori, but Tobio assures him that Issei is doing his best so Tobio decided to accompany him and the two share a fist-bump.

In Volume 25, Tobio has expressed an interest of wanting to face him and Vali, if he gets matched up with them, shocking Issei.

Lavinia Reni
They first meet in Volume 21, where Issei was fascinated by Lavinia’s beauty which caused Issei to get a headache after she was smiling at him (due to his illness at the time). They meet again in Volume 24, Where Issei was enchanted by her singing voice, much to Rias’s dismay. Issei gain lecherous thoughts about Lavinia upon gazing on her large breasts, which causes Rias, Ravel, and Rossweisse to glare at him. Lavinia later showed Issei a notebook containing Vali’s words that she wanted to show to Vali’s rival and was happy that Issei was praising Vali.

Natsume Minagawa
They first meet in Volume 24, when the Slash/Dog Team were on guard for any Grim Reapers to interrupt the Rating Game between Rias and Vali's teams. She is a fan of Issei's Oppai Dragon TV show and was really excited to meet him.

Kouki Samejima
Another member of Tobio's team who Issei met during Rias and Vali's Rating Game. They appear to on good terms in general, Kouki introduced himself while also relating with Issei by saying that he also likes big breasts.

Odin
They have seem have a friendly terms to each other. Odin acknowledges Issei's strength and power, also he sees Odin as very powerful leader of the Norse Faction.

Indra
Indra and Issei do not really have interactions to each other. But Indra seems to acknowledge his power and strength, but at the same time Sakra will not hesitate to eliminate Issei alongside his soul if he will be a threat to the world. Which is why Azazel protects Issei from Sakra from their inside matter. Indra considered Issei as a clown for his heroic efforts as Oppai Dragon despite being a Devil.

Despite all his initial problems with him, Indra helped Issei increased his powers by giving him Amrita so he can manifest Ddraig to make the Azazel Cup more interesting.

Hades
Like Azazel, Issei seems to dislikes Hades ever since he met him in the beginning. He hates him knowing the fact that Hades despises Devils and Fallen Angels and for secretly helping the Khaos Brigade from behind the scenes.

His hatred against him increased after his Grim Reapers attacked Koneko, Kuroka and his parents, stating he will not hesitate to defeat him and his allies if they continue to cause trouble.

Shiva
They met in Volume 22, where he greets and congratulates Issei for his promotion to a high-class devil. He also revealed and read Issei's real thoughts and where Ophis was at. He also asked Issei to join his side to fight Indra in the future, much to Issei's shock. Though he didn't answer Shiva directly, the two of them seem to have gotten along well and Shiva promised Issei that the two of them will have a good relationship and that he will protect him from behind.

Mahabali
Issei met him in Volume 22, alongside Shiva to personally congratulate him, also asking him to help them fight Indra in the future. The two of them seem to have gotten along well and Mahabali seemed to have an interest in fighting along side Issei or having a duel with him in the near future.

Sun Wukong
He first met Sun Wukong during his intervention with the Hero Faction, allowing him to overpower several members of the Hero Faction including their leaders. He assisted Issei using his Senjutsu to badly injured Cao Cao and help him to bring back Yasaka's consciousness. They seen have a friendly and good relationships as he volunteered himself to be Vali and his mentor to be strong and have achieved that equal to a God class opponents.

Shalba Beelzebub
Issei hated Shalba for his past action to Asia. Because of Shalba's growing insanity and his viewing Ophis as merely a tool to raise his own power, Issei's hatred towards him only grows stronger. When Shalba views the world has rejected him and tries to destroy the underworld and kill the children using Bandersnatch and Jabberwocky, Issei recognizes that he has basically gone insane and outright kills him to save Ophis and protect the children. This would make Shalba the first person Issei himself has ever actually killed. Ironically Shalba managed to use Samael's poison to finish Issei off as well but, unfortunately for Shalba, Issei's soul survived despite his body being destroyed and would later receive a new body.

Euclid Lucifuge
Euclid is Grayfia's younger brother as well as Rizevim's right hand man. Issei and Euclid's relationship was immediately hostile, as the latter is responsible for attempting to abduct the first year members of the Occult Research club and sending several wizards to attack them and finally even aiding in the revival of the Evil Dragons.

Furthermore, a little later on, both Issei and Ddraig developed a personal grudge against Euclid for creating a replica of the Boosted Gear from the remains of Issei's previous body and sacrificing the souls of famous dragons, an act even Vali seems to be appalled by. During their fight in Volume 16, Euclid was able to overpower Issei's Cardinal Crimson Promotion with his own Scale Mail armor in its normal Balance Breaker state, this is stated to be because Euclid's natural strength is equivalent to a Satan's even without the armor. Issei was able to turn the tables on Euclid only after using his newly awakened power and further theories that Euclid is observing him in order to learn how to use more of his techniques.

During their rematch in Volume 17, Issei was able to overpower Euclid by making the white wyverns into red that are able to use Ddraig powers which shocks him and the latter was defeated by Issei by unlocking Longinus Smasher thus defeating him and destroying his armor in process.

Cao Cao
Cao Cao and Issei start off with an initially hostile relationship due to the former being a leader in Khaos Brigade and for abducting Yasaka. Cao Cao also defeated Issei fairly easily during their ensuing battle and caused him to awaken his Illegal Move Triaina ability. Following their confrontation Issei did manage to rob Cao Cao of one eye, which would ultimately be replaced by an eye of Medusa. Issei's dislike of him is furthered when he attacks him and his friends, later to take Ophis' power away from her. Cao Cao himself, however, seems to hold Issei in fairly high regard during their later confrontations, especially after Issei returns from the dead, which even manages to make Cao Cao believe he can only be a true monster as he came back with Great Red which according to Cao Cao can't be referred to as luck. Issei's earlier wounding of Cao Cao's eye continued to be a factor even in their final battle, as Issei managed to use Samael's poison on his Medusa's eye and cause him near fatal levels of pain.

In Volume 18, they have seen have no antagonistic relationships and supporting each other and promised that someday they will fight once and settle the score between them, showing that have become more like rivals than enemies.

In True Volume 3, the two converse in Kyoto about Cao Cao's actions and motivations as Cao Cao shows remorse for his previous ways due to seeing that both supernatural beings also live in peace and have lives of their own, in contrast to his previous desire to drive away the supernatural which is the enemy of humans. After Issei states that Cao Cao having the ability to protect others due to the power of his True Longinus is amazing, Cao Cao states that him and Siegfried might have chosen a different path had they meet Issei earlier. Cao Cao asks Issei if he can become Issei's friend which he agrees, to Cao Cao's delight as the two strengthened their camaraderie before their battle with Erebus.

Elmenhilde Karnstein
Upon their first meeting, Issei disliked Elmenhilde for her intention to take Gasper for his ability and was angered when she discriminated Issei for claiming him to be nothing more than a mere servant with no qualifications, despite being the Red Dragon Emperor. After the events that traumatized her in Volume 16 and reunited in Worldly Desires of Steel short story after he saved from a stray devil and touched by his kindness, her selfish demeanor has lowered and they seem to have developed a friendlier relationship, with Elmenhilde appearing to have also developed feelings for him. Eventually her feelings for Issei is what led her to join his team for the Azazel Cup. While having a picnic with the members of Issei's and Rias's peerages, Elmenhilde listened in on the girls' stories of Issei saving them while taking down notes of the "criteria" needed to get Issei's attention. At the end of the volume she watched alongside Le Fay Pendragon as Issei's brides fought over him and wondered how she could get into the fight.

Valerie Tepes
She and Issei have shown to be on good terms with each other, as shown in volume 20 when she comforted Issei when he was being worried about Ravel.

Ddraig
Ddraig is the Dragon known as the Red Dragon Emperor that is inside Issei's Sacred Gear/Longinus, Boosted Gear. He gets along with Issei very well and Issei never thought of him as a tool, but later on when everyone starts calling him the Oppai Dragon, he becomes extremely depressed due to his credit being demolished little by little, going so far as to require medicine and counseling for the depression. He has a great interest in Issei due to him never giving up and protecting the ones he loves, also for being the possessor who talks to him the most and not seeing him as a tool. When he was with Issei when he died, he was devastated and told Ophis he was the greatest possessor of him, although he comes back along with Issei.

Tannin
Tannin is the Dragon that Issei trained with in the Underworld. He was the one responsible for helping him become stronger and attain his Balance Breaker. Issei and Tannin have such a close relationship that Issei calls him "Old-man Tannin". The two are really good friends and have fought numerous battles with each other. He was, at one time, a Dragon King and knew Ddraig before he was sealed. Issei has great respect for him and states that Tannin is the ideal Dragon King.

Ophis
Ophis officially met Issei at his house when Azazel invited her over to talk. At first, he was afraid of her because he thought she would destroy them immediately. Although she has no intentions other than to defeat the Great Red and return to her birthplace in the Dimensional Gap. At first, she took a huge interest in Issei because of how Ddraig was and reacted with Issei and how his color had changed from red to crimson. In Volume 11, Issei became Ophis' first friend, and he invited her to live with him in the Hyoudou Residence. Ophis is also Issei's last friend (according to Ddraig) prior to his reincarnation as a humanoid Dragon. In Vol. 12, she plays a big role in reviving Issei with the Great Red's help, and now stays with Issei. In Vol. 20, Issei is shown to care deeply for Ophis as he became enraged when she was attacked by Níðhöggr and Ophis shown to care fondly for Issei, as Issei was her first friend and wants to help him. Thus helping Issei by lending him Ophis's own power which enables him to unlock Diabolos Dragon which is so great that it overwhelms Rizevim Livan Lucifer's Sacred Gear Canceler, previously thought to be impossible.

Ophis is similar to a child mimicking everything she sees, as she has often wanted to do things normally done by the other loving members of the Gremory group to lssei.

Great Red
The relationship between Issei and the Great Red is somewhat vague, as Great Red rarely communicates with anyone and most of the communication between the two has been through Ddraig. However, Great Red was willing to save Issei and Ophis when the pocket dimension they were in collapsed, hurling them into the Dimensional Gap. He also crafted a new body for Issei from his own flesh.

Because Issei's present body has been made from the Great Red's flesh, Issei can merge with his power with no effort. Issei thinks of Great Red as almost like a super-powerful delinquent because of his tendency to just fly around the Dimensional Gap and taking offense at being glared at. Issei is also embarrassed by Great Red's apparent fondness of the Oppai Dragon theme song, a line of which is the only words directly exchanged between the two.

Crom Cruach
At first they were antagonistic to each other, but at the time of Volume 20, he no longer possesses any bad thoughts that lingering towards Crom Cruach. As it's seen when Issei bows his head and apologize to him for accusing him in what happens to Ophis, but Crom Cruach says there's no need for a Heavenly Dragon to bow his head to an Evil Dragon like him.

Lilith
Their relationships are somewhat vague, as they usually don't show any signs of antagonism to each other. Lilith seems to be interested in Issei, knowing that he possess Ddraig, as shown when she leaves the Qlippoth to see Issei again as well as another her (referring to Ophis) and Great Red. After moving into the Hyoudou Residence, Lilith became attached to Issei as she starts to sit on his lap, competing with Koneko and Ravel over it.

Apophis
Their first meeting seems to be antagonistic, were Issei thinks that he is a very brutal evil dragon but this proven wrong when Apophis mentions that he disdain and distaste of brutality and barbaric acts to Evil Dragons like Grendel and Níðhöggr. After their battle Issei respects him due for Apophis having an honorable side although he done so many evil things. Shortly before his death, Apophis promised to return someday and fight against him again.

Bova Tannin
Issei meets Bova in the Kuoh town's underground in Volume 22. Issei was shocked to learn he is Tannin's third son and the strongest amongst the children. Bova has shown greatly he respects Issei and the only one who hasn't given him a bad attitude. Bova wishes to stay by Issei's side as his subordinate rather than his servant. Eventually, Bova became a member of his team for the Azazel Cup. Bova even calls Issei "My lord".

Feeling ashamed to not be more useful for him in the previous match against Rias, he started to train with Crom in order to become stronger for Issei’s sake.

Tiamat
Issei first meets Tiamat at the Occult Research Club when Ouryuu and Millarca introduced her in Volume 23. When Tiamat demand to Ddraig to give back her treasure he borrowed, Issei tells Ddraig to give it back to her, which Tiamat tells Issei should also take responsibility as well, as he is the current possessor of the Boosted Gear. After that Tiamat warns Ddraig that she will not hesitate to burn him and Issei if he runaway like he always did, much to Issei's shock. He eventually becomes her guarantor until he wins the tournament and wishes to bring her treasure back.

Yasaka
In Volume 9, he helped save Yasaka from the Hero faction, using her leyline to summoned Great Red, after the hero faction retreat, he then help Kunou to wake her mother`s consciousness using his bilingual, with Sun Wukong assistance. They met once again in volume 19, where she entrusted Kunou to him and attempted to seduce him to have children with her, by Kunou`s protested to have little brothers or sisters much to Kunou`s annoyance. They both have friendly relationships.

In True Volume 2, Yasaka becomes one of Issei’s brides attending the wedding ceremony in the vision Chichigami made for Issei, hinting Yasaka will fall in love with Issei and become one of his future brides along with her daughter Kunou.

In True Volume 3, Yasaka started to show her feelings for Issei when watching him with Rossweisse and replaced her to make babies after she fell asleep. Later she appeared in the same bath that Issei saying that she wanted to increase his fighting spirit before the battle as his partner via sex and wanting to have his child. She also revealed be lonely, wanting a gentleman in her life and sought Issei to bare a child while convincing Kunou to accept it as she watch them until they're interrupted by Rias and Akeno.

Kunou
At first, she was under the impression that Issei kidnapped her mother and attacked him and his friends. After he saved her mother from the Hero Faction in Kyoto, Kunou developed a crush on Issei and told him she would always wait for him. Kunou began living with Issei sometime after Volume 19. Kunou becomes somewhat territorial towards Issei when her mother flirts with him. She hopes to grow up with breasts as big as her mother's to attract Issei.

In True Volume 3, Kunou started to fear losing Issei to her mother and becoming his daughter if he marries Yasaka, getting upset at her mother for making advancements towards Issei while Yasaka tried to calm her saying that it wouldn't be any problem.

Matsuda and Motohama
They are Issei's two closest human friends and fellow members of the Perverted Trio. The three will often get together and perform such activities as peeping and watching/reading porn. However, when push comes to shove, the two are completely willing to leave Issei to his own devices and receive their share of the punishment. Both of them are unaware of Issei's secret life as a Devil, he two have become very jealous of Issei's new found popularity with the ladies and take great joy in starting bad rumors about Issei and beat him up when enraged, Issei has been left out of their usual perverted activities because of his busy life that he passes off as club activities to them.

In Volume 22, Issei revealed to them that he is officially dating Rias, a news that caused them both to cry out blood, since then they have kept his relationship with her a secret from the whole school.

Despite his current rocky relationship with them, Issei does seem to care for them almost as much as anyone close to him, as he has stated that if possible, he would want to remain friends with them for the rest of his life.

Aika Kiryuu
Issei always complains about Kiryuu that she always teaches/tells to the Church Trio erotic things thinking that is one bad influence for them. After learning that she is now friends with Tosca and that she taught her a lot of things, he fears that she can be influenced for her and turn into a pervert girl. However, when not at odds, she tends tease him and Matsuda and Motohama, the two are on relatively good terms with her eating lunch at school alongside the Perverted Trio, Church Trio and Rossweisse.

In Volume 19, it is revealed that she is aware of the truth about Issei and his friends after summoning Xenovia and learned more about them from Rias, but assures to keep it a secret from everyone, showing a certain degree of trust. Afterwards his relation with her improved a little and now talks with some members of the ORC sometimes or even visiting Hyoudou Residence. When Issei was thinking enrolling in the Kuoh Academy University she was mentioned with some of his friends like Kiba, the Church Trio and Matsuda and Motohama with similar opinion that they would also enter university.

In True Volume 1, Issei learns that she is learning magic from Lavinia and asked Issei not to tell Asia and the others until she has improved her magic enough, he does so and thanked Lavinia for taking care of her.

Kiyome Abe
She met Issei when Rias needed to write a report about Youkai in Volume 8, but she didn't want to do it because she feared that she might lose her soul should she get involved with Devils. However, she agreed to do it if the Occult Research Club could prevail over her team in a tennis match, with the conditions being that if Rias lost, she would have to give up Issei temporarily. Unfortunately for her, she lost and had to write the report. Later on, she asked Issei to help her break an engagement that her father set up. Issei decided to help her in a battle of beasts against her father and in the process of helping her, fell in love with him.

Ouryuu Nakiri
They first meet in Volume 22, Ouryuu has been wanting to meet Issei for a long time and been asking his student council president Xenovia to meet him. When they meet, Ouryuu expressed his admiration towards Issei, despite him being a normal high school student and was put into many dangerous situation, Issei overcame it all and his possession of the Boosted Gear of the Welsh Dragon.

Under Tiamat's approval, Ouryuu joins Issei's team for the Azazel Cup as his "Fist of the Red Dragon Emperor of the Blazing Truth" and chooses to become his pawn after hearing that Issei originally began as pawn. Upon training together, Issei was impressed at Ouryuu's physical prowess and combat skills. After watching Issei comforts Ravel, Ouryuu respect and admiration for him grew to the point that he wishes to do better for him in future international rating games. During the morning training in True Volume 2, Ouryuu express his wish to become like Issei and gain the power to protect a girl.

Suzaku Himejima
Issei first meets Suzaku in Volume 24, where they are on friendly terms after Akeno and Ouryuu was under Issei’s care. Suzaku was satisfied when Issei agrees to make Akeno happy, after she was under the cruel treatment of the Himejima Clan.

Gorou and Miki Hyodou
Despite the fact that Issei constantly complains about his parents, Issei does love them deeply. In Volume 4 when Vali mentioned that he should try killing Issei's parents, Issei was so mad that he wanted to kill Vali on the spot. His parents are like any normal parents, who are very proud of and love their son dearly. Issei's mother even went on about how she was worried that Matsuda and Motohama were a very bad lecherous influence on Issei.

As of Volume 20, his parents found out about his secret life, and in spite of that, they still accepted their son as he is. However, both of them also seem to be slightly perverted, with Issei's father having had a dream of a harem when he was younger, and his mother not minding when she thinks Issei and Asia are having sex in the kitchen, even stating she wished she could peep at them. To Issei’s surprise his parents and his harem girls parents are starting plans for Issei and his harem girls weddings.

Juzo Hyoudou
Issei Grandfather Juzo was also described to be very perverted. It's implied that both his son and Issei’s perversion and desire for a harem must have been an influence from Juzo, with Issei missing him. Years after his death Issei achievements and the Oppai Dragon improved his life in the Buddhist Heaven with him talking with important deities about his grandson childhood and enjoying his life in the heaven with the Oppai Dragon song in the background which he has been singing and dancing every day in bliss.

After talk with her grandson in the Volume 24 he thanked him for it and praising Rias and even encouraging Issei in his harem king dream to obtain each beautiful girl that desires him or if he desires her.

Issei’s Grandmother
She liked Asia as Issei’s girlfriend when she met her encouraging Asia in her relation with Issei. Issei thinks that he should teach to her grandmother about the supernatural beings starting with something like the Nekomata Sisters for not scare her.

Touji Shidou
Irina's father that used to be Issei's neighbor, and was like an uncle to him. They seem to have a friendly relationship. Touji approves of his daughter's feelings for Issei, in fact he encourages them to have children so he can be a Grandfather and offers his full support, which usually leaves the two embarrassed. Touji has complete trust in Issei that he is able to protect his daughter.

Mrs. Shidou
Irina's mother and old neighbor who he viewed as an aunt. They appear to have a friendly and familial relationship even after not seeing each other in years, she also supports her daughters relationship with him, thus having complete trust in Issei.

Morisawa
Issei's first interaction started off rocky with Morisawa, doubting Issei's abilities as a Devil and preferring Koneko over him. However, they soon bonded over their childhood love of Drag So-Ball (a parody on "Dragon Ball") and ended up establishing a strange albeit friendly relationship over popular anime and games. When Morisawa was interested in meet one non-human girl and he met Christie dissapointed for her appearance cursing Issei but then they became in good friends.

Mil-tan
Despite Issei's continual apprehensiveness around Mil-tan, he considers him to be a nice person and they appear to have a good relationship. He even thanked to Lavinia to take care of him despite he continues shocked for his actions.

Elsha
Elsha is the second strongest and the strongest female Boosted Gear possessor. Issei considered her a beauty. The two meet each other in Volume 9 where she and Belzard help both him and Ddraig to awaken his newfound powers, and also support the two of them from the depths of Boosted Gear. They seem to have a good relationship to each other. Although they have only met for a short period of time, Elsha and Belzard say their final words after they vanish while smiling at Issei.

Belzard
The strongest Boosted Gear possessor that defeated two White Dragon Emperors in his lifetime. He alongside Elsha, help Issei and Ddraig to awaken their newfound powers. He sings the Oppai Dragon song while leaving with a smile along with Elsha.

Past Boosted Gear Possessors
At first, all of them didn't have interest in supporting Issei, and forced him to go berserk in Volume 10. But after Issei vanquished the curse and promised to them that he will show the future, they continue to support Issei until Volume 11 and 12 where they sacrifice themselves to save Issei's soul from Samael's curse.

Past Divine Dividing Possessor
It is revealed in Volume 10 that a Divine Dividing possessor resides in the Boosted Gear when Issei uses Albion's jewel where some of his thoughts resides. He helped Issei to reduce and halve the negative emotions and the curse of the Juggernaut Drive that covered the past Boosted Gear possessors. Though Issei doubted at first that he would help him, the possessor just smiled, and said that he is an interesting guy and counting that he will lead both the Two Heavenly Dragons. He and the rest of the past seniors of Boosted Gear sacrifice themselves in order to save Issei from Samael's curse.