My friend's wife is a lewd tutor

Yumi, a former gym instructor, decides to tutor Kazuhiko, a friend of her husband's, on dieting because he has recently gained weight. The study that started as a lecture gradually turned into practice, and the two of them were in agony as their sweaty bodies came into close contact. And Yumi, who has completely gone into erotic mode, seduces Kazuhiko with a color trick...