Onii-chan, Asa made Zutto Gyutte Shite!

Based on the erotic game by Tinkle Position, this OVA follows a young man who lives with his four younger sisters. During his childhood, he suffered from severe asthma, prompting his siblings to establish a comforting nightly routine: one sister would sleep beside him each night to keep him company, rotating among them on a daily basis so that he was never alone. As time passes, their parents—both working as researchers—introduce an unconventional directive tied to their latest experiment. Believing that physical affection can strengthen his immune system, they instruct him to hug whichever sister is sharing his bed that night for ten seconds before going to sleep. The goal is simple yet intimate: to improve his health through daily warmth and closeness. Taking his parents' instructions to heart, the protagonist decides to embrace the sister assigned to him that evening far more affectionately than she could have ever anticipated. What begins as a prescribed health measure quickly evolves into something much deeper, blurring the lines between familial care and unexpected intimacy as the nightly ritual takes on a life of its own.