Oniichan wa Oshimai! (Onimai: I'm Now Your Sister!)

Self-professed "home security guard" Mahiro Oyama has not left his home in years, secluding himself in his room playing erotic visual novels. This depraved lifestyle causes his prodigious sister, Mihari, to worry about his well-being. In hopes of solving this problem, she devises a plan to rehabilitate him back to normalcy. The first part of Mihari's plan is to concoct a medicine that changes her brother's biological constitution into a bona fide female, much to Mahiro's vehement dismay. Stuck in this predicament, Mahiro has no choice but to live out his life as a cute girl until the effect wears off—if it ever does. [Written by MAL Rewrite]

Onii-chan wa Oshimai! (ONIMAI: I'm Now Your Sister!) · AniList

MegaHouse G.E.M. series figure announced of Oyama Mahiro (Tenohira ver.) From Onimai: I'm Now Your Sister! (Onii-chan wa Oshimai!) : r/AnimeFigureNews

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

Oniichan wa Oshimai! (Onimai: I'm Now Your Sister!)

Onimai: I'm Now Your Sister! - Part 1 Blu-ray (Oniichan wa Oshimai!) (Japan)

low res anime on X: Source: Oniichan wa Oshimai! (Onimai: I'm Now Your Sister!) / X

ONIMAI: I'm Now Your Sister! New Clip and Release Date Announced! - Serpentor's Lair

Onimai: I'm Now Your Sister! Wallpapers - Wallpaper Cave

ONIMAI: I'm Now Your Sister! TV Anime Sets January 2023 Release with 1st Trailer - Crunchyroll News

ONIMAI: I'm Now Your Sister!