Yohei lives happily with his mother, Kaho, and his cousin, Fumika. However, one day, Kaho reveals to Yohei that she is actually his father's older sister, not his mother. She also informs him that his biological mother passed away a long time ago. Yohei is shocked by this news, but he begins to view Kaho as a woman rather than as his mother. Days later, a woman named Ikue moves into the house next door. When Ikue first sees Yohei, she suddenly starts crying, and Kaho turns pale. Ikue tells them that she is a relative of Yohei's mother and wishes to take him in as an adopted child. Naturally, Kaho and Fumika refuse this proposal. From that day on, their lewd and erotic life begins...