Kaiju No. 8

Kaiju No. 8 (怪獣8号), also known in English as Monster #8, is a Japanese manga series written and illustrated by Naoya Matsumoto (manga artist). It has been serialized on Shueisha's Shōnen Jump+ app and website since July 2020, with its chapters collected in 13 volumes as of July 2024. Shueisha has also published the series digitally on its Manga Plus service in English and several other languages. Viz Media began publishing the series digitally in August 2020 and has published the series in print in North America since December 2021.

The story follows Kafka Hibino, who after ingesting a parasitic creature, gains the ability to turn into a, he must now navigate using his power while trying to become part of an organization that eliminates kaiju to fulfill a promise he made with a childhood friend.

An anime television series adaptation produced by Production I.G aired from April to June 2024. A sequel has been announced. The series has spawned a light novel, two spin-off manga series, and a video game.

By July 2024, the manga had over 15 million copies in circulation. The series has been praised for its premise, story, characters, and art.

Setting
Kaiju No. 8 is set in a world in which monsters named regularly cause disasters. Japan has the highest rate of kaiju attacks in the world, therefore in order to combat them it establishes the Anti-Kaiju Defense Force (日本防衛隊). Kaiju are assigned a "fortitude level"—a scale indicating their overall strength, and are classified as honju—more dangerous, stronger kaiju, and yoju—smaller kaiju that can accompany or sprout off from honju. Kaiju that have high fortitude levels or abnormal characteristics are given a number as an identifier based on when they first appear, and are classified as.

Defense Force officers wear powered suits made from kaiju remains that grant them increased strength, speed, and durability. The suits have a total power output, measured in the form of a percentage (referred to as "unleashed combat power"), which varies from person to person (depending on their ability), with a maximum of 100%. The suits also influence how strong an officer's weapons are.

Daikaiju remains are used to create stronger weapons named Numbers (ナンバーズ) that are named after the daikaiju they are made from, but only a select few can use them if they are deemed compatible. Numbers weapons are much stronger than regular suits and provide their users with special abilities. The Defense Force consists of field officers led by platoon leaders, with varying levels of unleashed combat power, and captains and vice-captains whose combat power exceeds 90% and who lead divisions. Field officers are supported by a team of operators who provide information on kaiju, and monitor the field officers' health and suit output.

Plot
After their town is destroyed by kaiju, childhood friends Kafka Hibino and Mina Ashiro both vow to become members of the Defense Force to fight kaiju together. Mina, now 27, has since become the captain of the Defense Force's Third Division while Kafka, now 32, has failed the examination numerous times and works as a member of a clean-up crew that disposes of kaiju remains after battle. Kafka meets a young part-time worker in his company, Reno Ichikawa, an aspiring Defense Force member, who reignites his desire to become part of the Defense Force. However, a parasitic creature enters Kafka's body through his mouth and he gains the ability to turn into a kaiju. After escaping from the Defense Force, Kafka is given the code name "Kaiju No. 8" and decides to apply while keeping his kaiju form a secret.

Kafka and Reno pass the exam and join the Third Division along with Kikoru Shinomiya, a kaiju-slaying prodigy who Kafka saved during the test from a humanoid kaiju which the Defense Force names "Kaiju No. 9". Kafka encounters No. 9 once more when it tries to kill Reno during their first mission with the Third Division. Kafka fails to kill No. 9 and as he tries to hide he is attacked by the vice captain of the Third Division, Soshiro Hoshina. After a short fight, Kafka escapes from the vice captain, still maintaining his cover. However, Kafka is eventually forced to reveal his kaiju form when he transforms in front of the Third Division to save its base in Tachikawa from destruction after it is attacked by another humanoid kaiju named Kaiju No. 10.

Kafka is, reluctantly, apprehended by Mina and sent to Defense Force headquarters where he is given a chance to prove his usefulness after he defeats the Director General of the Defense Force, and Kikoru's father, Isao Shinomiya, in a duel. Kafka and Kikoru join the First Division led by captain Gen Narumi where they again fight No. 9 who attacks Shinagawa. Although the group kills two decoy versions of No. 9, the real one attacks Isao and absorbs him and his Numbers 2 weapon, a powered suit of armor created from the remains of Kaiju No. 2, with which it becomes stronger. No. 9 escapes and prepares for an invasion of Japan. Kafka and Kikoru train for the invasion with Kikoru gaining her mother's Numbers 4 weapon. Reno gains the Numbers 6 weapon and trains with the Fourth Division.

Several months later, No. 9 begins its invasion of Japan, sending a group of kaiju identified as Kaiju Nos. 11–15 that attack Gen, Soshiro, Kafka, Mina and Kikoru respectively. After some struggle, Gen, Soshiro, Kafka, and Kikoru succeed in defeating their opponents with Mina being the last one to defeat hers. However, No. 9 uses the corpse of Kaiju No. 14 as a portal to close the distance between itself and Mina, revealing its plan to kill and absorb Mina in order for it to gain her highly destructive ability that makes her an important part of the Defense Force. Kafka tries to reach Mina but is stopped by numerous kaiju controlled by No. 9. However, Reno arrives to clear a path for Kafka who manages to reach Mina before she is absorbed by No. 9. Kafka and No. 9 begin their battle.

Main

 * Kafka Hibino (日比野 カフカ) / Kaiju No. 8 (怪獣8号)
 * A 32-year-old man with dreams of joining the Defense Force to fight alongside his childhood friend Mina Ashiro. He gives up on his dream after failed, past attempts to join the Defense Force and starts working in a kaiju disposal company as a cleaner. He gains the ability to turn into a kaiju after a small, parasitic creature (voiced by Tarako) enters his body through his mouth. After escaping from the Defense Force he is subsequently dubbed "Kaiju No. 8." In his kaiju form, Kafka possesses superhuman strength, speed, durability, regeneration, and the ability to detect other kaiju. He has a fortitude level of 9.8, making him the most powerful kaiju identified by the Defense Force. Due to the low unleashed combat power of his suit he utilizes his knowledge of kaiju anatomy from his work in the disposal industry to help his squad-mates defeat kaiju.
 * Kafka's predicament in the series was partly inspired by the author's career struggles in creating manga. Kaiju No. 8's design was inspired by depictions of  while the design's blue glow was inspired by the film Tron (1982).
 * Kafka's predicament in the series was partly inspired by the author's career struggles in creating manga. Kaiju No. 8's design was inspired by depictions of  while the design's blue glow was inspired by the film Tron (1982).


 * Reno Ichikawa (市川 レノ)
 * An 18-year-old man who starts working in the same company as Kafka with plans to join the Defense Force. He becomes friends with Kafka and helps him hide the secret of his kaiju form. Reno is a considered to be a promising recruit and quickly becomes one of the Defense Force's strongest assets and joints the Fourth Division after the destruction of the Third Division's base. He is compatible with the Numbers 6 weapon made from the remains of Kaiju No. 6 that has a fortitude level of 9.6 and that devastated the Defense Force prior to the events of the series. The Numbers 6 weapon takes the form of a suit of armor that increases Reno's strength and speed and gives him the ability of cryokinesis.
 * An 18-year-old man who starts working in the same company as Kafka with plans to join the Defense Force. He becomes friends with Kafka and helps him hide the secret of his kaiju form. Reno is a considered to be a promising recruit and quickly becomes one of the Defense Force's strongest assets and joints the Fourth Division after the destruction of the Third Division's base. He is compatible with the Numbers 6 weapon made from the remains of Kaiju No. 6 that has a fortitude level of 9.6 and that devastated the Defense Force prior to the events of the series. The Numbers 6 weapon takes the form of a suit of armor that increases Reno's strength and speed and gives him the ability of cryokinesis.


 * Kikoru Shinomiya (四ノ宮 キコル)
 * A young woman who joins the Third division together with Kafka and Reno. A kaiju-slaying prodigy, Kikoru is one of the greatest talents in the Defense Force and has the highest recorded unleashed combat power as a recruit. Her father, Isao, is the Director General of the Defense Force while her mother, Hikari, was a captain who died in the line of duty while fighting off a kaiju invasion led by Kaiju No. 6 prior to the events of the series. She uses a giant axe as her personal weapon and inherits her mother's Numbers 4 suit which gives her increased speed and the ability of flight.
 * A young woman who joins the Third division together with Kafka and Reno. A kaiju-slaying prodigy, Kikoru is one of the greatest talents in the Defense Force and has the highest recorded unleashed combat power as a recruit. Her father, Isao, is the Director General of the Defense Force while her mother, Hikari, was a captain who died in the line of duty while fighting off a kaiju invasion led by Kaiju No. 6 prior to the events of the series. She uses a giant axe as her personal weapon and inherits her mother's Numbers 4 suit which gives her increased speed and the ability of flight.

Executives

 * Isao Shinomiya (四ノ宮 功)
 * The Director General of the Defense Force and Kikoru's father who is considered to be one of the strongest combatants in the history of the Defense Force. Isao uses the Numbers 2 weapon made from the remains of Kaiju No. 2 in the form of a powered suit of armor and gauntlets, which gives him superhuman strength and the ability to use blasts that extend his attack range. Isao begins teaching Kikoru how to fight against kaiju after the death of his wife, Hikari. Isao tests Kafka in battle and spares him from disposal so that he can be used as an asset for the Defense Force. During one of Kaiju No. 9's attacks on Tokyo, Isao is killed and absorbed by No. 9.
 * The Director General of the Defense Force and Kikoru's father who is considered to be one of the strongest combatants in the history of the Defense Force. Isao uses the Numbers 2 weapon made from the remains of Kaiju No. 2 in the form of a powered suit of armor and gauntlets, which gives him superhuman strength and the ability to use blasts that extend his attack range. Isao begins teaching Kikoru how to fight against kaiju after the death of his wife, Hikari. Isao tests Kafka in battle and spares him from disposal so that he can be used as an asset for the Defense Force. During one of Kaiju No. 9's attacks on Tokyo, Isao is killed and absorbed by No. 9.


 * Keiji Itami (伊丹 啓司)
 * Itami is the dutiful Deputy Director of the Defense Force, and is later appointed the Director after Shinomiya's demise at No. 9's hands.
 * Itami is the dutiful Deputy Director of the Defense Force, and is later appointed the Director after Shinomiya's demise at No. 9's hands.

First Division

 * Gen Narumi (鳴海 弦)
 * The captain of the First Division of the Defense Force and its strongest active captain. Gen uses the Numbers 1 weapon made from the remains of Kaiju No. 1. The weapon takes the form of a powered suit of armor and a pair of retinal implants that give Gen the ability to predict enemy movements allowing him to always land his attacks. His personal weapon is a large rifle with a bayonet.
 * The captain of the First Division of the Defense Force and its strongest active captain. Gen uses the Numbers 1 weapon made from the remains of Kaiju No. 1. The weapon takes the form of a powered suit of armor and a pair of retinal implants that give Gen the ability to predict enemy movements allowing him to always land his attacks. His personal weapon is a large rifle with a bayonet.


 * Rin Shinonome (東雲りん)


 * A platoon leader in the First Division who highly respects Gen. She uses a minigun as her weapon of choice.

Second Division

 * Jura Igarashi (五十嵐 ジュラ)
 * Jura Igarashi is the Captain of the Second Division of the Defense Force. He is also Hakua Igarashi's older brother.

Third Division

 * Mina Ashiro (亜白 ミナ)
 * The 27-year-old captain of the Third Division of the Defense Force. She is Kafka's childhood friend with whom he vowed to fight against kaiju. She is one of the strongest officers in the Defense Force and is highly skilled in using firearms due to a unique ability making her shots more devastating compared to other captains. Her personal weapon is a handheld cannon, making her effective against giant-sized kaiju.
 * The 27-year-old captain of the Third Division of the Defense Force. She is Kafka's childhood friend with whom he vowed to fight against kaiju. She is one of the strongest officers in the Defense Force and is highly skilled in using firearms due to a unique ability making her shots more devastating compared to other captains. Her personal weapon is a handheld cannon, making her effective against giant-sized kaiju.


 * Soshiro Hoshina (保科 宗四郎)
 * The vice-captain of the Third Division. He is a skilled swordsman who is good at fighting smaller kaiju. Soshiro is frequently advised by his superiors to quit being a field officer due to his ineffectiveness with firearms. Mina, however, values his skill as a swordsman and asks him to become her vice-captain. On Soshiro's recommendation, Kafka is retrained as a cadet in the Third Division. Secretly, Soshiro suspects that Kafka is hiding something since the Third Division registered a 9.8 fortitude level at the same time that Kafka's suit stopped working when he transformed during the aptitude test to save Kikoru from a honju. In the battle against Kaiju No. 10 Soshiro stalls the fight long enough for Mina to incapacitate it after which it is turned into a Numbers weapon that is compatible with Soshiro. This weapon takes the form of a sentient suit with a tail that can be used for attacks.
 * The vice-captain of the Third Division. He is a skilled swordsman who is good at fighting smaller kaiju. Soshiro is frequently advised by his superiors to quit being a field officer due to his ineffectiveness with firearms. Mina, however, values his skill as a swordsman and asks him to become her vice-captain. On Soshiro's recommendation, Kafka is retrained as a cadet in the Third Division. Secretly, Soshiro suspects that Kafka is hiding something since the Third Division registered a 9.8 fortitude level at the same time that Kafka's suit stopped working when he transformed during the aptitude test to save Kikoru from a honju. In the battle against Kaiju No. 10 Soshiro stalls the fight long enough for Mina to incapacitate it after which it is turned into a Numbers weapon that is compatible with Soshiro. This weapon takes the form of a sentient suit with a tail that can be used for attacks.


 * Iharu Furuhashi (古橋 伊春)
 * A new recruit who joins the Third Division together with Kafka, Reno and Kikoru. He and Reno become part of the same platoon and develop a rivalry over the course of their training.
 * A new recruit who joins the Third Division together with Kafka, Reno and Kikoru. He and Reno become part of the same platoon and develop a rivalry over the course of their training.


 * Haruichi Izumo (出雲 ハルイチ)
 * A new recruit of the Third Division, Haruichi is the scion of the Izumo family who run the Izumo Tech corporation that develops equipment for the Defense Force.
 * A new recruit of the Third Division, Haruichi is the scion of the Izumo family who run the Izumo Tech corporation that develops equipment for the Defense Force.


 * Aoi Kaguragi (神楽木 葵)
 * A JGSDF officer who joins the Third Division and becomes part of the same platoon as Haruichi.
 * A JGSDF officer who joins the Third Division and becomes part of the same platoon as Haruichi.


 * Konomi Okonogi (小此木 このみ)
 * The lead operator of the Third Division who provides information to field officers. Her operations team monitors the suit power output of officers and can also remove their limiters allowing the officers to use greater outputs.
 * The lead operator of the Third Division who provides information to field officers. Her operations team monitors the suit power output of officers and can also remove their limiters allowing the officers to use greater outputs.


 * Akari Minase (水無瀬あかり)
 * Akari is a Defense Force officer of the Third Division.
 * Akari is a Defense Force officer of the Third Division.


 * Hakua Igarashi (五十嵐ハクア)
 * Hakua is a tall Defense Force officer with blue hair in the Third Division. She is also Jura Igarashi's younger sister.
 * Hakua is a tall Defense Force officer with blue hair in the Third Division. She is also Jura Igarashi's younger sister.


 * Tae Nakanoshima (中之島 タエ)
 * Nakanoshima is a platoon leader in the Third Division of the Defense Force, who is into younger guys. Haruichi and Aoi are part of her platoon.
 * Nakanoshima is a platoon leader in the Third Division of the Defense Force, who is into younger guys. Haruichi and Aoi are part of her platoon.


 * Ryō Ikaruga (斑鳩亮)
 * A platoon leader of the Third Division. Reno and Iharu are part of his platoon.
 * A platoon leader of the Third Division. Reno and Iharu are part of his platoon.

Fourth Division

 * Jūgo Ogata (緒方ジュウゴ)
 * The captain of the Fourth Division of the Defense Force. He trains Reno and Iharu when they join the Fourth Division after the destruction of the Third Division's base and oversees Reno's training with the Numbers 6 weapon.

Kaijus

 * Kaiju No. 9 (怪獣9号)
 * A humanoid kaiju who can create other kaiju and absorb humans, taking their appearance and memories. No. 9 infiltrates society by initially disguising itself as a human kaiju cleaner named Takamichi Hotaka (voiced by Tomokazu Sugita). No. 9 orchestrates most of the catastrophes that befall the Defense Force. It absorbs Isao Shinomiya and his Numbers 2 weapon which greatly increases its strength and ability to create stronger kaiju. No. 9 is constantly in the pursuit of knowledge and aims to create a world for kaiju to thrive in.
 * A humanoid kaiju who can create other kaiju and absorb humans, taking their appearance and memories. No. 9 infiltrates society by initially disguising itself as a human kaiju cleaner named Takamichi Hotaka (voiced by Tomokazu Sugita). No. 9 orchestrates most of the catastrophes that befall the Defense Force. It absorbs Isao Shinomiya and his Numbers 2 weapon which greatly increases its strength and ability to create stronger kaiju. No. 9 is constantly in the pursuit of knowledge and aims to create a world for kaiju to thrive in.


 * Kaiju No. 10 (怪獣10号)
 * A humanoid kaiju that leads an attack on the Third Division's base leading a group of wyvern kaiju. It is ultimately defeated by Soshiro and Mina and is apprehended by the Defense Force. While imprisoned, No. 10 reveals that its creator is Kaiju No. 9 and asks to be turned into a Numbers weapon to be used by Soshiro. It is the first kaiju to be made into a Numbers weapon while still alive, retaining its sentience. No. 10 has a maximum fortitude level of 9.0.
 * A humanoid kaiju that leads an attack on the Third Division's base leading a group of wyvern kaiju. It is ultimately defeated by Soshiro and Mina and is apprehended by the Defense Force. While imprisoned, No. 10 reveals that its creator is Kaiju No. 9 and asks to be turned into a Numbers weapon to be used by Soshiro. It is the first kaiju to be made into a Numbers weapon while still alive, retaining its sentience. No. 10 has a maximum fortitude level of 9.0.

Production
Naoya Matsumoto (manga artist) began his career in 2006 with Neko Romancer, a series that was published in Jump Giga (then known as Akamaru Jump). He authored a series titled Nekowappa! that debuted in Shueisha's Weekly Shōnen Jump in 2009. The series was a continuation of a one-shot that Matsumoto wrote for the JG1 One-Shot festival. He published another one-shot titled Shikai Enbu in the 2012 spring edition of Jump Giga (then known as Jump Next) before starting his second serialization with Pochi Kuro that debuted on Shueisha's Shōnen Jump+ application and website in 2014. Matsumoto presented the idea and general outline of Kaiju No. 8's story to deputy editor-in-chief of Shōnen Jump+, Seijiro Nakaji, near the end of 2018.

Matsumoto said that Kaiju No. 8 was influenced by media such as the Ultraman series, specifically Ultraseven (1967), as well as Shin Godzilla (2016) and Pacific Rim (2013). Matsumoto aimed to create a story that follows a protagonist who has to achieve their goal while hiding their identity from a hostile organization they are also a part of, seeing it as an entertaining concept and described Kaiju No. 8 as "a challenging work" that allowed him to move away from his usual stories. According to Nakaji, Kaiju No. 8 was an unexpected development from Matsumoto's usual fantasy stories saying that Matsumoto was drawn to protagonists of the  genre "who gain extraordinary abilities, and become [heroes], but also bear the weight of inner struggle as a consequence." Nakaji said that they planned to progress the story in two ways: "[o]ne where Kafka leads a normal life while hiding his true identity, and the other where he pursues his dream even after becoming a monster" with Matsumoto opting for the latter choice early on. Matsumoto aims to create page layouts that are easy to follow, especially on smartphones, due to the manga being released digitally. Nakaji said that they try to take advantage of the series' digital release giving an example of a panel in the second chapter of the series which was completely in color, something that would not be possible if the series was being published in a physical magazine. Matsumoto draws inspiration from mythological creatures, animals and plants when designing kaiju. The codenames that are given to kaiju were inspired by typhoon categorization on the advice of a coworker who pointed out that this would make the kaiju appear more as disasters.

Matsumoto works with three assistants for the series: Osamu Koiwai who is responsible for background art, Jiro Sakura who does "finishing work" and Mantohihi Binta who is credited for weapon design. For background art, Matsumoto prepares a storyboard providing compositions of the panels of a chapter that are sent to Koiwai. They discuss how to approach the scene after which Koiwai prepares a draft for Matsumoto's approval. Once the draft is approved Koiwai can proceed with producing the final version of the backgrounds. It takes Koiwai 3–4 days to complete the backgrounds of a chapter. Koiwai shares the process of creating backgrounds on YouTube.

Manga
Written and illustrated by Naoya Matsumoto (manga artist), Kaiju No. 8 started on Shueisha's Shōnen Jump+ application and website on July 3, 2020. In August 2020, Matsumoto and Kaiju No. 8 adopted a schedule where a new chapter is published every week for three weeks, followed by a one week break. From June 25, 2021, a new schedule was adopted where a new chapter is published every two weeks. Shueisha has collected its chapters into individual volumes. The first volume was released on December 4, 2020; a promotional video for the volume, presented as a news program, was shown on the big screen of Yunika Vision at Seibu-Shinjuku Station from December 4–10, 2020. As of July 4, 2024, 13 volumes have been released.

Viz Media began publishing the series in English on its website on August 2, 2020, under the title Kaiju No. 8, and on February 19, 2021, it announced that it had licensed the series for print in English, releasing the first volume on December 7, 2021. Shueisha began publishing chapters of the series on its Manga Plus website and app on July 22, 2020, under the title Monster #8 in English and several other languages. On March 30, 2023, Manga Plus announced that it would include Kaiju No. 8 in the title of the version of the manga on its service.

To promote the release of the first volume in France, publisher Crunchyroll (then known as Kazé) displayed a mural on the Bibliothèque Nationale in Paris from October 6–15, 2021. The series is licensed in Italy by Star Comics, the publication of which was commemorated by the display of a mural in the Porta Genova metro station in Milan. The series is also licensed in Spain by Planeta Cómic, in Argentina by Editorial Ivrea, in Taiwan by Ever Glory Publishing, and in Poland by Studio JG.

Chapters not yet in tankōbon format
These chapters have yet to be published in a volume. They were serialized on Shōnen Jump+.
 * Chapter: 105–111

Kaiju No. 8: B-Side
A spin-off manga illustrated by Kentaro Hidano, titled Kaiju No. 8: B-Side (怪獣8号 side B) ran from January 5 to July 12, 2024, on Shōnen Jump+. The spin-off is based on the light novel Kaiju No. 8: Exclusive on the Third Division, written by Keiji Andō, and features side stories of Defense Force members. Shueisha and Viz Media began publishing the series in English on January 4, 2024, Shueisha on its Manga Plus website and app and Viz Media on its Shonen Jump website and app. Shueisha has collected its chapters into individual volumes. The first volume was released on April 4, 2024. Viz Media licensed the series for print in English with the first volume set to be released in Q2 2025.

Chapters not yet in tankōbon format
These chapters have yet to be published in a volume. They were serialized on Shōnen Jump+.

Kaiju No. 8 Relax
Another spin-off manga, illustrated by Kizuku Watanabe, titled Kaiju No. 8 Relax, began its serialization in Saikyō Jump on June 4, 2024, and on Shōnen Jump+ on June 7 of the same year.

Light novel
A 4-chapter side story light novel titled Kaiju No. 8: Exclusive on the Third Division (怪獣8号　密着！第3部隊) written by Keiji Andō and illustrated by Matsumoto, was released on November 4, 2022. On February 2, 2024, Viz Media announced that it had licensed the light novel for print in English. It is set to be published in Q4 2024.

Anime
On August 4, 2022, it was announced that the manga would be receiving an anime adaptation, later revealed to be a television series produced by Production I.G, with Studio Khara supervising the designs and artworks. It is directed by Shigeyuki Miya and Tomomi Kamiya, with scripts by Ichirō Ōkouchi, character designs and chief animation direction by Tetsuya Nishio, art direction by Shinji Kimura and monster designs by Mahiro Maeda. The series aired from April 13 to June 29, 2024, on TV Tokyo and its affiliates, alongside Twitter for simulcast in Japan.

Crunchyroll licensed the series for streaming, alongside livestream simulcasting as it airs in Japan, as well as dubbed versions an hour after its television premiere, which includes English, Brazilian Portuguese, French, German, Italian, Spanish, Latin American Spanish, Hindi, Telugu, and Tamil. Medialink licensed the series for streaming in Southeast Asia on its Ani-One Asia YouTube channel.

After the airing of the final episode, a sequel was announced. Crunchyroll will stream the sequel.

Music
The music was composed by Yuta Bandoh creating a film score for the series. Bandoh worked with various artists such as (sic)boy, Taiiku Okazaki and LEO Imai to compose original songs for the anime. The soundtrack also features music by "The Kaiju Band", a musical project created for the anime consisting of guitarist Takayuki "Kojiro" Sasaki, King Gnu bassist Kazuki Arai and drummer Shun Ishikawa. American artists Patrick Paige II of The Internet and Suni MF are also featured on the soundtrack which was released on June 26, 2024. The opening theme song is "Abyss" performed by Yungblud, while the ending theme song is "Nobody" performed by OneRepublic.

Other media
Kafka Hibino is featured as a playable character in the video game Captain Velvet Meteor: The Jump+ Dimensions that was released on the Nintendo Switch on July 28, 2022.

A life-size statue of Kafka's kaiju form was displayed at the Tachikawa Station on the Chūō Main Line from April 26–29, 2024. Kafka's voice actor Masaya Fukunishi was appointed as the ceremonial one-day manager at the Kaiju No. 8 store in the station. The statue was displayed in four other places from May 1 to June 16, 2024.

A video game project, tentatively titled Kaiju No. 8: The Game, was announced in June 2024. It is developed by Akatsuki Games and is set to be available for smartphones and Windows (via Steam).

Popularity
According to Yūta Momiyama, the deputy editor-in-chief of Shōnen Jump+, Kaiju No. 8, along with Spy × Family, have been very popular and are doing especially well on the Manga Plus service. In December 2020, it was reported that Kaiju No. 8 surpassed 30 million views, making it the fastest Shōnen Jump+ series to achieve this feat, and each new chapter published surpasses one million views. In February 2021, the series reached 70 million views. In April 2021, the series reached over 100 million views. In February 2023, the series reached 400 million views. The series ranked tenth on AnimeJapan's 5th "Most Wanted Anime Adaptation" poll in 2022.

Manga
The School Library Journal listed the first volume of Kaiju No. 8 as one of the top 10 manga of 2021. It ranked third on Takarajimasha's Kono Manga ga Sugoi! 2022 list of best manga for male readers. The series ranked second on the Nationwide Bookstore Employees' Recommended Comics of 2022. The series was included in Polygons list of the best comics of 2021, Kotaku's list of the 11 best manga series of 2021 and The Fandom Posts list of the 12 best manga series of 2020.

Sales
The series' first volume sold 90,831 copies in its first week, and 69,404 copies in its second week. By December 2020, the first volumes had over 430,000 copies in circulation (print and digital). In January 2021, it was reported that the series was the best-selling new manga of 2020, within only 28 days since the first volume was published. By March 2021, the manga had over 1 million copies printed physically and 200,000 copies sold digitally, making it the fastest Shōnen Jump+ series to reach 1 million copies in circulation, and 20 days later reached 1.5 million copies in circulation. By June 2021, the manga had 2.5 million copies in circulation, and by middle of the month it reached 3 million copies. By September 2021, the manga had over 4 million copies in circulation; over 5.5 million copies in circulation by December 2021; over 6.7 million copies in circulation by March 2022; over 7.8 million copies in circulation by July 2022; over 8 million copies in circulation by August 2022; over 10 million copies in circulation by December 2022; over 11 million copies in circulation by March 2023; over 13 million copies in circulation by April 2024; over 14 million copies in circulation by June 2024; and over 15 million copies in circulation by July 2024.

The series' fifth and sixth volumes were among the 30 best-selling manga volumes of 2022. Volume 9 was among the best-selling manga volumes of 2023. Volume 10 was Shueisha's seventh highest first print run manga volume of 2023–2024 (period from April 2023–March 2024), with 600,000 copies printed.

Individual volumes have ranked on Circana (formerly NPD) Bookscan monthly list since 2021 NPD Bookscan monthly list:
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 * June 2024: and on The New York Times' Graphic Books and Manga bestseller monthly list since 2022. The New York Times' Graphic Books and Manga bestseller monthly list:
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 * July 2024: The series' first volume sold 118,000 copies in the United States in 2022.

In France, the series sold 22,041 copies in its first week, making it the best-selling debut of manga in France. By April 2023, the series sold 888,888 copies in France. In Italy, the first volume had a first print run of 245,000 copies (including various editions), surpassing Demon Slayer: Kimetsu no Yaiba, which has 200,000 copies in circulation per volume.

Critical reception
The series' first volume has been positively received by various publications. Praise has been aimed at Naoya Matsumoto's artwork, which has been described as "gorgeous and incredibly detailed", and at his use of page spreads and kaiju designs. Kafka Hibino has, particularly, been singled out as an endearing character and a novel aspect of the series due to his age. The series has also been lauded for its comedy. However, the first volume received some criticism for its formulaic beginning as well as inconsistent art quality and fast pacing that sacrifices character development. With its premise, protagonist and kaiju designs, the series has drawn comparisons to the Ultraman series.

Anime
The series' premiere was positively received. In a series of positive reviews for Anime News Network, Rebecca Silverman praised the art, animation and music saying that the series treads familiar territory but that "it's very comfortably working within the bounds of its genre and having fun with them." James Beckett complemented Production I.G for successfully balancing comedic elements of the story with "wonderful and weighty little beats that sell the entire world that much more effectively." Nicholas Dupree praised the show's action sequences and worldbuilding, noting that Kafka is a character who is easy to root for while Richard Eisenbeis praised the animation, specifically the detailed and realistic depiction of kaiju fights and their dissection, although he found the character designs to be simplistic. Digital Spy's Janet A Leigh praised the series' premiere for its animation and action, comparing its premise to Attack on Titan but with a more light-hearted tone. Toussaint Egan of Polygon similarly described the series' premise as a combination of My Hero Academia and Pacific Rim while praising its tone, dramatic moments, action and art direction.

Grant Jones of Anime News Network wrote positively about the first season with high praise for the season's second half. Episode 6 ("Sagamihara Neutralization Operation at Daybreak") provided story elements that expanded upon the world of the series. Episode 8 ("Welcome to the Defense Force") was a highlight due to a well animated fight scene between Kafka and Soshiro, for providing depth to supporting characters and for increased tension due to Kafka's secret identity nearly being revealed. Episode 10 ("Secret Revealed") was praised for the surprising development of Kafka revealing his kaiju form to the Defense Force as Jones expected this to happen much later. The final two episodes were praised for their overall presentation in terms of animation, direction and storyboarding with the eleventh episode ("Kaiju No. 8 Captured") bringing the "visual fidelity to the highest levels in the season thus far" while the final episode ("Kafka Hibino") provided an effective cliffhanger for the second season. Criticisms of the season were aimed at the character designs which were described as "rather bland" and "very flat." Episode 3 ("Revenge Match") was seen as a low point of the season due to its reliance on tropes and its "lackluster" animation. Isaiah Colbert of IGN wrote positively of the first season saying that even though the series follows standard tropes of "other shōnen anime," its balance of action and drama allowed for "character-rich moments" that added depth and intrigue to the story.