"I can't ask anyone but my mother!" Koji, whose relationship with his girlfriend isn't going well because he's bad at sex, begs his mother, Reimi, to be his sex practice partner. Naturally, Reimi refuses. There's no way that such an act can be tolerated. However, when she is unable to resist his reckless caresses, and when he forces her, coupled with her weak masochistic nature, Reimi comes unwillingly. Then, Reimi quietly tells Koji, "It's okay if it's just once."