After losing her husband, Yumi has been raising her son, Nobuyuki, on her own. Recently, it seems that her son has found a girlfriend, and while she has mixed feelings about it, she secretly watches over him. One day, her son confesses to her that he is unable to satisfy her because of his premature ejaculation. Worried, Yumi decides to give her son sexual training. She tries to get him used to the stimulation with handjobs and blow jobs, but Nobuyuki's premature ejaculation does not improve, so Yumi decides to use her own body to teach her son about sex...