My friend's wife is a lewd private tutor

Hitomi is asked by her husband's friend to tutor her son. Hitomi, who can't refuse when asked, teaches Koichi how to study, who is currently a two-timer, but Koichi is only concerned about Hitomi's breasts and doesn't concentrate on her studies. Eventually, he starts saying that he will study if he lets him touch his breasts. Hitomi makes Koichi touch her breasts, but her desire gradually escalates...