On the verge of giving birth, Keita's wife returns to her parents' home, leaving him behind to manage the household alone. Though lonely, he resolves to stay strong for the sake of their unborn child. Suddenly, his sister-in-law, Fumina, shows up unannounced. "I'm already here, so let me help you with the chores," she says, eagerly offering assistance. Her warmth eases Keita's loneliness, but as their time together increases, his rationality begins to waver. While telling himself that family is what matters most, he finds his heart drawn to Fumina's voluptuous body and irresistible charm, gradually losing control over his desires.