The story of two pairs of mothers and sons. Tatsuo Onai, a son who lives alone while attending a university in the Tokyo metropolitan area. For home renovations, his cousin Masaru Shinomiya and aunt Shinomiya Chiaki are staying at his mother Yukaori Onai's house—essentially, Tatsuo's childhood home. One day, Tatsuo returns home as planned but cannot contain his sexual excitement towards his mother, leading to multiple acts of intercourse and ejaculation inside her. Around the same time, Masaru is also in a forbidden master-servant relationship with his own mother, Chiaki. They then witness the incestuous act between Tatsuo and his mother.
