Her only son is shy about sex, let alone a girlfriend. Unable to bear this, his mother, Rei, decides to use her own body to give him a sex education, so that he doesn't gain any wrong sexual knowledge. At first, she only teaches him how to masturbate and gives him handjobs while breastfeeding, but after having sex with him, which she had only intended to be a one-time thing, Rei remembers the joys of being a woman. Having experienced this pleasure, her son desires his mother's body even more, and continues to thrust into her with all his might.