One year ago, Reiko remarried and entered the household as a beautiful and kind mother. The new family consists of her husband, her stepson Yuuma who is a college student, and herself. Reiko is masturbating in the Japanese-style room when Yuuma, walking down the hallway, accidentally sees her. During dinner, Yuuma honestly confesses that he saw his mother masturbating. Reiko becomes unsettled, and later during sex with her husband, she cannot concentrate, eventually lashing out in anger. After having sex with her husband, Reiko finds herself thinking about her son and heads toward his room. Suddenly, Yuuma embraces her and begins making advances. Hesitant at first, Reiko ultimately gives in and has sex with her stepson. An unexpected relationship develops between mother and son, leading to a shocking series of events.