Onimai

Onimai: I'm Now Your Sister!

Company type	Manga series
Industry	Manga, Anime
Founded	2017
Founder	Nekotofu
Headquarters	Japan
Area served	Japan, North America, Asia-Pacific
Products	Manga, Anime television series

is a Japanese manga series created by Nekotofu. Initially published online in 2017, it began regular serialization in Ichijinsha's Monthly Comic Rex magazine from April 2019 onward and is officially licensed in English by Kodansha USA. An anime adaptation produced by Studio Bind aired between January and March 2023, garnering strong viewership ratings despite receiving mixed reviews internationally.

Plot

Mahiro Oyama, a reclusive otaku and NEET residing with his scientist sister Mihari, wakes up one day to find himself transformed into a young girl as a result of one of Mihari's scientific experiments. He must learn to live as a middle school girl while coming to terms with his altered identity.

Characters

Originally an otaku male, Mahiro undergoes a gender transformation due to Mihari’s experiment and enrolls in middle school. He has a passion for video games and led a mostly isolated lifestyle prior to the change.

Mihari is Mahiro’s younger sister and a gifted scientist responsible for the transformation. She advanced through school rapidly and is currently attending university.

Mihari’s classmate from middle school, Kaede is a gyaru known for her culinary and makeup skills. She also holds a part-time job at a fast food establishment.

Kaede’s tomboyish younger sister, Asahi is Mahiro’s peer and has admired him for years. She shares a long-standing friendship with Kaede.

An energetic classmate of Mahiro’s who struggles academically and often assigns nicknames to him.

A fellow student with an interest in yuri themes who frequently imagines romantic situations involving her friends. She is notably more busty than her peers and feels self-conscious about it.

A bright yet introverted second-year student, Nayuta is the ward of Mihari’s university advisor Chitose Azuma. Tasked with covertly observing Mahiro on Azuma’s behalf, she quickly becomes integrated into Mahiro’s circle of friends.

Mihari’s senior at university and Nayuta’s guardian, Azuma played a key role in creating the drug that caused Mahiro’s transformation. She leverages Mihari to further her own secretive objectives, using Nayuta to discreetly monitor Mahiro.

Production

Prior to developing this series, Nekotofu was an admirer of the "gender bender" genre in anime and manga, drawing inspiration from works such as Ranma ½, Kashimashi: Girl Meets Girl, among others. Motivated by the film Your Name and positive responses to a gender-bending doujinshi he had produced, Nekotofu began self-publishing Onimai on Pixiv in January 2017. The series later expanded its presence on Niconico Seiga, where it gained substantial popularity. From April 2019, the manga was serialized in Ichijinsha's Monthly Comic Rex. Nekotofu continues to self-publish online works and doujinshi with permission from Ichijinsha.

Manga

Created by Nekotofu as both writer and illustrator, Onimai: I'm Now Your Sister! first appeared online on platforms such as Pixiv in 2017. Its serialization began in Ichijinsha's Monthly Comic Rex magazine on April 27, 2019. As of July 2025, Ichijinsha has issued ten tankōbon volumes. In North America, the series is digitally distributed in English by Kodansha USA.

Anime

On April 22, 2022, it was revealed that an anime television series adaptation would be produced by Studio Bind. The project features Shingo Fujii as chief director, Michiko Yokote overseeing the script as head writer, character designs crafted by Ryo Imamura, and a musical score composed by Daisuke Achiba alongside Alisa Okehazama. This anime was broadcast from January 5 through March 23, 2023, across AT-X and additional channels. The opening song, titled "Identeitei Meltdown" (アイデン貞貞メルトダウン), is performed by Enako featuring P Maru-sama. The ending theme, "Himegoto*Crisisters" (ひめごと＊クライシスターズ), is delivered by Marika Kōno, Kaori Ishihara, Hisako Kanemoto, and Minami Tsuda. For global audiences, Crunchyroll provided streaming access, while Medialink secured licensing rights for the Asia-Pacific region.

Awards and Rankings

Onimai: I'm Now Your Sister! secured the fifth position in Da Vinci's Next Manga Award 2018 under the web manga segment and ranked ninth in the Web Manga Overall Election 2019. Additionally, it achieved third place in AnimeJapan's 2020 Manga We Want to See Animated poll and followed with a seventh-place finish in the same category in 2021.

Critical Response

During Winter 2023, this series emerged as Japan’s highest-rated TV anime on platforms such as Niconico and Anikore.jp. Japanese critics commended its musical score, artistic design, and meticulous portrayal of daily life, distinguishing it among contemporary anime offerings.

Initial English-language critiques presented a mixed outlook despite favorable audience ratings. While some reviewers pointed out contentious subject matter, the animation quality and soundtrack consistently received acclaim. Rebecca Silverman characterized the fan service as "moderately restrained" but found the storyline’s premise somewhat difficult to fully appreciate.

Anime News Network’s Kim Morrissy delivered enthusiastic endorsement, naming Onimai the standout anime of the season and lauding its storytelling, comedic elements, artwork, and Shingo Fujii’s direction. Though Sakugablog acknowledged the series across several categories for the Sakugabooru Animation Awards 2023, it ultimately did not secure any awards.

Fan Engagement

In February 2023, admirers of Onimai demonstrated considerable enthusiasm by sending a variety of gifts to Studio Bind, the studio responsible for the anime’s production. Director Shingo Fujii shared images of these offerings on Twitter, expressing appreciation for the fans’ active involvement.