After seeing off his wife who returned to her parents' home for childbirth, Kota began living alone for the first time in a while. Gradually, he started feeling lonely without anyone to talk to. Seeing his condition, his wife's older sister, Yukari, pays him a visit. Struck by her voluptuous figure and outstandingly large breasts, Kota becomes overwhelmed and rushes into the bathroom to hide. However, Yukari catches him and forcefully lures him into the bedroom. As he grows increasingly intimate with his buxom and tender sister-in-law, Kota is drawn deeper into a forbidden relationship.