Tsukasa's hobby is collecting underwear. She wears her collection and indulges in fantasies in front of the mirror. However, her favorite sexy underwear is stolen. Suspecting her younger brother, Tsukasa sneaks into his room from the balcony. She finds him masturbating using Tsukasa's underwear. The next day, she searches his room but can't find him. With no other choice, she provokes him in her underwear to get him to talk. His brother is reluctant to confess, but she teases him sexually. From that day on, she begins to feel pleasure in dominating and sexually teasing him.