Yohei lives happily with his mother, Kaho, and his cousin, Fumika. But one day, Kaho tells Yohei that Kaho is actually his father's older sister, not his mother... She also tells him that his mother died long ago. Yohei is shocked to learn this, and begins to look at Kaho as a woman, not his mother. A few days later, the woman, Ikue moves into the house next door to them. When Ikue sees Yohei for the first time, she suddenly begins to cry and Kaho turns pale. Ikue tells them that she is related to Yohei's mother, and she wants to take him as her adopted child. Of course, Kaho and Fumika stop her... From that day on, their obscene and erotic life begins...