Oniichan wa Oshimai! — anime announcement about a guy who became a sister

Ichijinsha announced that a TV anime adaptation for ‘Oniichan wa Oshimai!’ (Onimai: I’m Now Your Sister!) is in the works. Along with the announcement, a teaser image, as well as the main cast and crew have all been revealed.

A promotional video was made to highlight the announcement and the release of the manga’s 6th volume:

Manga artist Nekotofu also tweeted their congratulations, noting that the announcement of an anime adaptation coincides with Mihari Oyama’s birthday:

本日はみはりちゃんのお誕生日です。プレゼントの中身はなんと…！？
『お兄ちゃんはおしまい！』突然のアニメ化決定！！
お陰様でついについに…！
順次情報が追加されるかと思いますので、アニメ公式を要チェック！
公式Twitter：@onimai_anime
公式サイト：https://t.co/Y6OBTABgI8#おにまい pic.twitter.com/xmZSOxoARk

— ねことうふ@アニメ化決定！6巻4/27発売 (@nekotou) April 22, 2022

The comedic manga was first published on Pixiv by Nekotoufu before being picked up by Ichijinsha for physical distribution.
It is being published digitally in English by Kodansha USA, who describes the plot as follows:

Mahiro Oyama was just a normal erotic-game loving dude…until he woke up one morning as a woman! Turns out his mad-scientist little sister, Mihari, tried out one of her new experiments on him…with a disastrous outcome, as far as Mahiro’s concerned! But Mihari is as determined to study him as he is determined to go back to his shut-in, game-playing life, and one thing’s for sure…life is going to get a whole lot weirder from here on out!

Main Cast

Role	Name	Previous Roles
Mahiro Oyama	Marika Kouno	Silence Suzuka (Uma Musume: Pretty Derby), Yumina Urnea Belfast (Isekai wa Smartphone to Tomo ni.)
Mihari Oyama	Kaori Ishihara	Shouta Magatsuchi (Kobayashi-san Chi no Maid Dragon), Aladdin (Magi: The Kingdom of Magic)

Staff

The following are the individuals and organizations who are involved in the production:

• Director: Shingo Fujii (Mushoku Tensei: Isekai Ittara Honki Dasu episode director)
• Series Composition: Michiko Yokote (Jahy-sama wa Kujikenai!)
• Character Design: Ryou Imamura (Yama no Susume Third Season opening animation director)
• Production: Egg Firm
• Studio: Studio Bind

Official site: https://onimai.jp/
Official Twitter: @onimai_anime