Young mother-in-law's secret sex education

Rin married Sentarou and became stepmother to Sentarou's child Manji from his previous wife at a young age. Manji grew up with his father always telling him about studies from an early age, and he had no knowledge of sex and didn't even know about masturbation. Partly because of this, Rin feels responsible as a mother to Manji, who stains his pants with wet dreams almost every day, and teaches him about women's bodies and sexuality, saying, ``Now, I'm going to teach you how to masturbate. Don't tell your father, and don't touch me either.''