To fulfill the wishes of clients seeking sexual relations with blood relatives, Kagi Takefumi launches a project. An older brother who raised his younger sister as a parental figure secretly harbors illicit desires for her and becomes the client. Under the pretense of celebrating her marriage, the sister is taken to a hot spring inn, where her brother pretends to pass out drunk. She is then seduced by an unfamiliar man and ultimately gives in. Hidden cameras capture the entire act as the sister, writhing her hips while whispering "We'll get caught," indulges in pleasure. She is repeatedly penetrated and brought to climax multiple times. Blindfolded and brought to another peak, the man suddenly switches places with her brother. Unaware of the switch, the sister moans in pleasure as her brother thrusts into her from behind.