Youhei lives a peaceful life with his mother Kaho, and cousin Fumika. One day, Kaho suddenly confesses to Youhei that she is actually not his mother by birth. Although this depresses Youhei, Kaho assures him that he can continue living with her and Fumika, whom he has always treated as a sister, as if nothing has changed. However, a woman claiming to be Ikue, younger sister to Youhei's actual birth mother, moves in next door and asks that Youhei moves in with her. While Youhei is in a state of confusion, the three women attempt to use their voluptuous bodies to seduce him.