Kenji, the undemanding middle son of three brothers, is left living alone with his mother Aoi after his older brother moves out for work, his younger brother enters a boarding school, and his father takes a distant assignment. The suddenly empty house leaves Aoi overwhelmed by loss. Hurt that she seems preoccupied with his brothers, adult-role-play Kenji grows determined to claim all of his mother's affection for himself, drawing the two into an incestuous relationship.