One day, teenage son Koji discovers an unfamiliar bikini while sorting through a pile of laundry. When he asks his mother Koharu about it, she initially avoids answering, but eventually blushes and quietly confesses, "That... is mine..." Koji pleads with her to wear it, and upon seeing his mother in the swimsuit, he loses all self-control. Her appearance now seems like that of a deviant sex addict.