During spring break, Ai Sayama's younger sister and her husband returned to their hometown to visit their family, although she is still unmarried, so she still lives at home with her parents. After a lavish feast, the night had fallen, everyone went back to their rooms to sleep, in the silent night, Ai heard her sister moaning when she had sex with her husband, that moaning made Ai unable to sleep, the desire for sex burned inside her, But she only knew how to masturbate right outside the partition of her sister's room.
What was even more surprising was that the very next day, Ai had the thought of stealing his sister's husband...