Two days after seeing off his wife who left for a trip, Kenichi returned home to find the living room in complete disarray. Suddenly, his wife's older sister, Kaho, appeared out of nowhere. Though surprised, Kenichi felt endless gratitude toward her as she kindly helped clean up the mess. In return, he promised to let her stay the night. While relaxing in the bathtub together, the naked Kaho suddenly attacked him from behind. "What are you doing, Onee-san!?" he protested, but the softness of her big tits pressed against his back made his cock instantly erect. As the situation spiraled further out of control, Kenichi found himself writhing in helpless agony.