Kasane Teto
Kasane Teto is a virtual singer with a voicebank for UTAU, a singing voice synthesizer software. The character was initially created as a joke for April Fools' Day 2008 on the Japanese textboard 2channel, but she was later made into an actual voicebank in the same year. Teto has been introduced as a "diva born from a hoax".
Along with the UTAU voicebank, Kasane Teto was released as a voice model in 2021 for TALQu, a text-to-speech software developed by Haruqa Software, in 2023 for Synthesizer V AI, in 2025 for VOICEPEAK, a text-to-speech software developed by AH-Software, and in 2025 for Synthesizer V 2 AI.
Character
Kasane Teto is officially stated to be 31 years old. In her earliest design, she was tall and weighed. She is listed as liking baguettes and having a tsundere personality.Kasane Teto is portrayed as a youthful girl with reddish hair styled in spiraling twintails resembling drill bits, a style her developers refer to as "twindrills." She typically wears a uniform-style outfit with a red and black color scheme, which has become a recognizable part of her image. Her personality is generally portrayed as mischievous.
History
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, with Oyamano Mayo as the voice provider. The first song using her voice was released on 1 June 2008.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.
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 as a part of Hatsune Miku's act in the Sapporo Snow Festival.Synthesizer V
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 Synthesizer V AI voice database for the character, its first full commercial release. On 3 April 2023, Kasane Teto AI version 104 was announced. 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 Synthesizer V 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". Synthesizer V AI Kasane Teto was released on 27 April 2023, and has received frequent updates. A limited "lite" voice database for the same software was released soon after on 8 May 2023, available for free download.On 30 October 2025, AH-Software announced a Kasane Teto voice database for Synthesizer V 2 AI, which was released on 27 November 2025.
VOICEPEAK
For Teto's 17th anniversary on 1 April 2025, AH-Software announced an adaptation of Kasane Teto's voice for their Japanese text-to-speech software, which was released shortly after on 24 April 2025.Voicebanks
Reception
Despite not being a Vocaloid character, Kasane Teto has gained popularity among Vocaloid and UTAU fans. Within six months of her release, more than 500 videos with the "Kasane Teto" tag were published on Niconico, and the song "" featuring Kasane Teto reached 100,000 views, entering the Vocaloid Hall of Fame. According to stats from the 2025 Music Awards Japan, 5 out of the top 10 most popular Vocaloid tracks in Japan featured Kasane Teto, notably surpassing Hatsune Miku who was featured in 3. Among songs nominated for the 2025 Best Vocaloid Culture Song award, Teto was the second most used voice behind Miku. Tetoris by Hiiragi Magnetite reached 105 million views, being the first and only solo Kasane Teto song to reach over 100 million views on YouTube.Notable songs
| Awards | Category | Song | Artist | Year | Result | |
| 2025 Music Awards Japan | Best Vocaloid Culture Song | "" | Yoshida Yasei | 2023 | rowspan="4" Nomitated | |
| 2025 Music Awards Japan | Best Vocaloid Culture Song | "" | 2024 | - | ||
| 2025 Music Awards Japan | Best Vocaloid Culture Song | "Mesmerizer" | Satsuki / 32ki | 2024 | - | |
| 2025 Music Awards Japan | Best Vocaloid Culture Song | "Tetoris" | Hiiragi Magnetite | 2024 | - |