A young and beautiful mother, Haruki, and her son, Shiro, can be seen as a couple from the outside, and they can talk about anything. However, even in such a parent-child relationship, the son, who has entered puberty, cannot talk about 'sex'. One day, the homeroom teacher informs him that Shiro brought an AV to school and became a problem. Haruki is troubled, and as a mother, she decides to teach her son about women's bodies and SEX using her own body. At first, the son is confused, but he is fascinated by the touch of his mother's lips and young and firm breasts, and finally, through the forbidden brush strokes, he comes to know the body of a woman.