Miwako, who has been raising her son on her own, one day hears her son confide in her a problem. He is unable to have good sex with his new girlfriend due to premature ejaculation. She wonders what she would have said to her if she had a husband, and before she knows it, she decides to train her son's penis with her own hands. The training, which began with helping him masturbate, soon turns into forbidden sex...