Ani Tomo (Brother's Friend) (2018)

Sota Nishino (Ryusei Yokohama) is a good looking high school student. He meets Mai who is his friend Yukihiro Nanase’s younger sister. She is also a high school student and somewhat naive. Sota Nishino mutters to Yukihiro Nanase "Your sister is cute." Mai overhears Sota's remark through the thin wall between her room and her brother's room.