While his wife is away visiting her parents, Konatsu, his sister-in-law, comes to stay and fill the void. Koji happily welcomes her long-awaited visit, laughter filling the rooms. However, everything changes the moment they head to the bath. Konatsu pleads, "Please don't come in, brother-in-law," but Koji insists on washing her back, and eventually the two end up soaking together in the tub. Overcome by her defenseless, beautiful figure, his desire becomes uncontrollable, and he gives in, having sex with her. This story captures the sudden shift in everyday life and the turmoil of emotions. Expect a thrilling, heart-pounding narrative where surprise and temptation collide.