Kasane Teto

Kasane Teto (Japanese: 重音テト) is a virtual singer software (known as a voicebank) created on the Japanese textboard 2channel for April Fools' Day, 2008. Although the software was initially created as a hoax and did not exist, it later was actually produced and made compatible with singing voice synthesis software, allowing it to sing. Teto was introduced as a "diva born from a hoax".

On 1 April 2008, Kasane Teto was revealed under the guise of a software release announcement page, along with a fake software demonstration using sample-edited vocals. At the time of the hoax's release, Kasane Teto had no actual software. However, soon after the free singing voice synthesis software "Utau" was made available by volunteers. This enabled users to make songs using her voicebank.

As a derivative character of Hatsune Miku, Kasane Teto gained popularity among vocaloid fans. On Niconico, Japan's leading video sharing service, the "Kasane Teto" tag exceeded 500 in six months, and the song "嘘の歌姫(Uso no utahime/A Fake Diva)", created using Kasane Teto, achieved 100,000 views and was inducted into the Vocaloid Hall of Fame.

The rights holders who provided the character design and voice of Kasane Teto established the circle "TWINDRILL" in 2009 to promote and manage the character. Although Kasane Teto was a parody character of Crypton Future Media's series of Vocaloid singers, Twindrill organised the rights and established a cooperative relationship with Crypton from 2009 to 2010. Since 2010, Crypton has been the point of contact for commercial use.

Since the rights were arranged, Kasane Teto has been active in many fields, including appearing in Sega's music game franchise "Hatsune Miku -Project DIVA-", becoming a promotional character for Hokkaido Broadcasting, obtaining Nendoroid and other plastic figures from Good Smile Company, performing with Nakamura Shidō II on the Kabuki stage, and publishing a novel motifed on Kasane Teto.

Kasane Teto was supported as a voice model in 2021 by TALQu, a deep learning-based free speech software, and in 2023 by Synthesizer V AI, a commercial singing voice synthesis software.

Character
Kasane Teto is a 31 years old chimera. In her earliest design, she was 159.5 centimetres tall and weighed 47 killograms. She is listed as liking baguettes and being a tsundere.

Creation
Kasane Teto's origins come from 2channel, a Japanese bulletin board. In 2008, a group of users devised a plan to make a fake Vocaloid character. Character names, hairstyles, genders, ages, likes, dislikes, special skills, and other traits were randomly selected from among the suggestions of 2channel users and consolidated into a single character, which would be shown as a prank for April Fools' Day. On 6 April 2008 she appeared for the first time on video, and on 13 April 2008, the first voicebank for Teto was released. The first song using her voice was released on 1 June 2008.

2010s and 2020s
Teto continued to make an impact on the vocaloid community with many songs being released. In 2012, a DLC pack for Hatsune Miku: Project Diva F featured her. In 2013, she appeared for Hatsune Miku's act in the Sapporo Snow Festival 2013.

SynthV
For the 15th anniversary of Teto on 1 April 2023, Japanese software developer AH-Software announced they would be partnering with Twindrill and Crypton Future Media to produce a "Synthersizer V AI" voice database for the character, its first full commercial release. For the occasion, a significant redesign was made, giving Teto a new outfit to stand apart from being a Hatsune Miku parody. The deep learning technology in SynthV made use of singing from the voice provider rather than concatenative phoneme samples like UTAU. This allowed for cleaner, more natural synthesis and various features such as "Vocal Modes" for expression and the ability to sing in any language that Synthesizer V AI supports via "cross-lingual synthesis". This voicebank was released on 27 April 2023 and has received frequent updates. A limited "lite" voice database for the same software would come soon after on May 8 2023, available for free download.

2023 and Beyond
While initially having a cult following, after the release of Kasane Teto AI, Teto received a surge of popularity. Multiple hit tracks were made using both the original UTAU software and Synthesizer V, and ranking Teto among the most used virtual singers of the year.