For a long time, Mikawaya had harbored romantic feelings for Erina, but one day, he caught her masturbating, causing his pent-up desire to explode uncontrollably. Overcome with lust, Mikawaya advances on Erina right then and there—but instead of resisting, she accepts him willingly. From that day on, the two begin a daily, increasingly lewd affair. However, their secret tryst doesn't last long, as her son soon discovers their actions, setting off a chain of unexpected events.