A mother named Ayano, who was abandoned by her parents and raised in an institution, dreamed of a happy life with her family of three, but was Kokoro by the conflict between her realistic husband Keiji and her son Takayuki, who was betting on his dream. Before her marriage, Ayano was taught the pleasure of anal sex by her boyfriend, who grew up in the same institution and looked up to her like an older brother. She has never been able to forget that taste, and she always has anal sex with her husband. Takayuki, who knew about the abnormal couple's activities, felt more than motherly feelings for Ayano, and eventually crossed the forbidden line...