While his career-focused wife is away on a long business trip, her older sister Ichika moves in and offers to handle the housework. Now he is alone with the woman he has secretly desired, unable to look away from the huge tits bouncing as she works. When he peeks into the bathroom, Ichika puts on a masturbation show and asks him to join her in the tub. Her unexpected invitation launches a forbidden marathon of bath sex that keeps going until the heat leaves them dizzy, complete with creampies.