While his wife is away on a trip to her hometown, the house is empty—until his sister-in-law, Chihiro Sayayama, suddenly shows up, claiming she's there to take care of him. Chihiro has been deeply dissatisfied with her married life and is desperate to release her pent-up desires immediately. She barges into the bathroom while her brother-in-law is showering and seduces him with her alluring, mature body. His willpower wavers, but the real question is what will happen to his cock. This unexpected visit ends up causing a dramatic shift in their family dynamics.