Rin marries Sen taro and becomes the young stepmother to his son from a previous marriage, Manji. Since childhood, Manji has been forced by his father to focus solely on studying, leaving him completely ignorant about sex—he doesn't even know what masturbation is. As a result, he experiences nightly wet dreams, soiling his underwear. Feeling responsible as a mother figure, Rin tells him, "From now on, I'll teach you how to masturbate. But it's our secret—don't tell your father, and you mustn't touch me." She gently and carefully educates him about the female body and sexuality. Her warmth and tenderness deeply affect Manji's heart.