Onimai

Plot

The series follows Mahiro Oyama, an otaku and NEET who lives alone with his scientist younger sister Mihari. One day he wakes up to find himself transformed into a young girl, a result of one of Mihari's experiments. Mahiro must now learn to become comfortable in his new body whilst living life as a middle school girl.

Characters

Mahiro Oyama (緒山 真尋, Oyama Mahiro)

Voiced by: Marika Kōno

The protagonist of the series, Mahiro was previously an otaku man living with his younger sister Mihari until he was turned into a girl as a result of one of her experiments. Mahiro ends up transferring to a middle school. Mahiro is fond of playing video games and mainly stayed at home before being turned into a girl.

Mihari Oyama (緒山 みはり, Oyama Mihari)

Voiced by: Kaori Ishihara

Mahiro's younger sister and a scientist. She turned Mahiro into a girl as a result of one of her experiments. Due to her high intelligence, she skipped several grades and is now a university student.

Kaede Hozuki (穂月 かえで, Hozuki Kaede)

Voiced by: Hisako Kanemoto

Mihari's classmate during middle school and a gyaru. She is Momiji's older sister. She is good at cooking and using cosmetics. She also works part-time at a fast food restaurant.

Momiji Hozuki (穂月 もみじ, Hozuki Momiji)

Voiced by: Minami Tsuda

Kaede's younger sister and Mahiro's classmate. She has a tomboyish personality and greatly admires Mahiro. She has been friends with Asahi for several years.

Asahi Ōka (桜花 朝日, Ōka Asahi)

Voiced by: Kana Yūki

Mahiro's classmate. She has an energetic personality but tends to not perform well in tests. She also calls Mahiro by many nicknames.

Production

Prior to creating the series, Onimai's author, Nekotofu, was a fan of the "gender bender" genre of anime and manga that included such works as Ranma ½, Kashimashi: Girl Meets Girl, and Idol Pretender. As such, Nekotofu had harbored a longtime interest in creating his own such series, and was inspired to do so after seeing Your Name. He was also motivated by the positive response to a doujinshi he had created which also featured similar gender-bending elements. Nekotofu began self-publishing Onimai on Pixiv in January 2017, and later on Niconico Seiga, where it became significantly more popular. In April 2019, the manga began serialization in Ichijinsha's Monthly Comic Rex magazine. Nekotofu continues to self-publish the series online and produce doujinshi with permission from Ichijinsha.

Media

Manga

Written and illustrated by Nekotofu, Onimai: I'm Now Your Sister! began serialization online via Pixiv and other platforms in 2017. It also started in Ichijinsha's Monthly Comic Rex magazine on April 27, 2019. As of May 2026, eleven tankōbon volumes have been released by Ichijinsha. In North America, Kodansha USA is publishing the series digitally in English.

Anime

An anime television series adaptation was announced on April 22, 2022. It is produced by Studio Bind and chief directed by Shingo Fujii, with Michiko Yokote as head writer, character designs handled by Ryo Imamura, and music composed by Daisuke Achiba and Alisa Okehazama. The series aired from January 5 to March 23, 2023, on AT-X and other networks. The opening theme song is "Identeitei Meltdown" (アイデン貞貞メルトダウン) by Enako feat. P Maru-sama, while the ending theme song is "Himegoto*Crisisters" (ひめごと＊クライシスターズ) by Marika Kōno, Kaori Ishihara, Hisako Kanemoto, and Minami Tsuda. Crunchyroll streamed the series. Medialink has licensed the series in Asia-Pacific.

Reception

Accolades

Onimai: I'm Now Your Sister! ranked fifth in Da Vinci's Next Manga Award 2018 in the web manga category in August 2018, and ranked ninth in Web Manga Overall Election 2019 in October 2019. The manga also ranked third in AnimeJapan's Manga We Want to See Animated Ranking in 2020, and ranked seventh in 2021.

Critical reception

The series received positive reviews and was ranked by viewers in Japan as the top-rated TV anime of the Winter 2023 season on both Niconico and anime ranking website Anikore.jp. One Japanese-language reviewer, writing for 4Gamer.net, echoed positive sentiments regarding its music and art style. Shoki Ota, writing for KAI-YOU, said the series was remarkable for its meticulous depiction of everyday life, and said, "While it might not be for everyone due to its gender swap themes, it feels like a condensed work amid the recent 'anime festival', making it a must-see this season".

In early English-language coverage of the series, the critical response to Onimai's first few episodes were mixed despite the high user ratings. Some reviewers criticized the first episode's premise and lolicon themes, and perceived incestuous overtones, while praising the animation and music, which was near-universally deemed to be of exceptional quality. Rebecca Silverman was softer in her criticisms, describing the fan service as "relatively toned down" but stated that the narrative premise was too "mean" for her to enjoy and squandering its potential.

Kim Morrissy, reviewing the anime for Anime News Network, was more positive, saying "Onimai is the best anime of the season." Morrissy strongly praised the narrative, humor, art, and animation production, particularly the work of series director Shingo Fujii, who previously worked on Precure. Sakugablog also mentioned Onimai multiple times in their Sakugabooru Animation Awards 2023 for Best Show, Best Animation Design, and other categories but did not give it any awards.

Popularity

In February 2023, fans of Onimai sent numerous gifts to the staff of Studio Bind, the production studio of the anime, which series director Shingo Fujii posted photos of in a tweet voicing thanks for the support.