When Daiki is asked to accompany his mother's close friend on a trip in her place, he finds himself in an unexpected situation. The woman introduced as his mother's friend turns out to be Miku—a stunning, big-breasted beauty, far from the ordinary middle-aged woman he imagined. Daiki sneaks into the bathroom, intending to use her lingerie for masturbation, but gets caught red-handed. As their private cohabitation begins, unforeseen complications arise.