Karina's strict parents give their adult daughter a 5 p.m. curfew, so their dates never go beyond cafés and museums before her father calls her home. Wanting more, her boyfriend accepts an invitation to her house and meets her beautiful, mature mother Satsuki. When Satsuki tells him to break up with Karina, he impulsively pins her down. From then on, he and Satsuki meet in secret for creampie sex aimed at giving Karina a little sister—always just after Karina leaves to make her curfew.