Tatsuo Ishibashi, a college student living in Tokyo, returns to his family home, where his mother Yuko Ishibashi resides with her brother-in-law Yohei Yagi, his son Yasuhiro Yagi, and her sister-in-law Azusa Yagi. Due to house renovations, the family temporarily lives together. Tatsuo had planned to bring his girlfriend home as scheduled, but overwhelmed by his feelings for his mother, he repeatedly engages in sexual acts with her instead. Meanwhile, Yasuhiro also ends up having a sexual relationship with his own mother. Eventually, the two sons discover each other's mother-son incestuous affairs. This story explores the boundaries of family bonds and morality.