Riho and her boyfriend, a working adult couple, decided to move into a new home as they started thinking about marriage. Excited for a happy future, Riho's peace of mind is shaken by a strange problem—her big, voluptuous ass seems to have a mind of its own, moving independently. At their new place, she meets Okada, a struggling student with an unhealthy lifestyle. Concerned, Riho—working from home—begins bringing him meals and taking care of him. Unfulfilled in her sex life with her boyfriend, Riho one day feels an intense itch in her ass while cooking lunch at Okada's place. Overcome with desire, her eyes lock onto Okada's thick cock, sparking a new, passionate relationship.