Her son, who is in the midst of puberty, masturbates every day. Reiko watches over him, thinking it can't be helped because he's at that age, but one day she finds out that the porn her son is wanking to is a mature woman AV with an actress the same age as her. This means that Reiko is faced with a cock that gets excited by older women like her. And it's an astonishingly energetic cock that gets hard again and again... There's no way Reiko, who is a slut by nature, can resist it.