Yukiko suffers from extreme loneliness and sexual frustration due to her husband Koichi's neglect. When her stepfather visits, he discovers her secret desires, leading to a provocative encounter that eventually draws Koichi into a twisted competition for her pleasure. In a shocking turn of events, the family's boundaries collapse as Yukiko finds a perverse sense of fulfillment in the shared attention of the two men.
Yuuki's secret relationship with Rio is exposed when Yukiko, the mother of the house, decides to join in on the pleasure. After seducing Yuuki and manipulating a distraught Rio into accepting their unconventional family dynamic, the household descends into a chaotic group encounter. Even the grandfather is eventually drawn into the fray, leaving Yuuki overwhelmed by the unexpected intensity of his new family bonds.