Because her boyfriend was sick and living alone, the younger sister brought him home to take care of him. She had to go out to buy medicine, leaving her boyfriend at home without knowing that her older sister, Honoka Tsuji, was using her big breasts to seduce her boyfriend. Despite resisting fiercely because she didn't want to betray her boyfriend, Tsuji continually used her breasts to tease him every day, as her younger sister didn't have such big breasts. Even when the younger sister slept next to her, Tsuji would sneak in at midnight and steal her sister's boyfriend...