After losing her husband, mother Yuu raises her only son, Ichiro, alone until she decides to remarry her late husband's former boss, Tamotsu. However, Tamotsu's teenage stepson, Yuki, becomes increasingly drawn to Yuu's mature and sensual body. One day, Yuki accidentally witnesses Yuu performing sexual acts on her biological son. From that moment on, his desire spirals out of control. He begins pressuring Yuu, saying things like, "I want to bathe with you," and "Do the same thing to me." Caught in this unusual triangle, Yuu gradually gives in to a forbidden affair with her stepson. As their illicit relationship deepens, emotions and desires intertwine, forging a new and twisted bond between them.