Reiko, married into a wealthy family, grew weary of her husband's indifference and cold demeanor. Meanwhile, she found herself drawn to her kind and empathetic son, Kousuke, harboring secret romantic feelings for him. Suddenly, Kousuke receives a letter revealing he was switched at birth and is not her biological son. Shattered by the truth, Kousuke falls into despair—but having long desired Reiko as a woman, his suppressed passion overwhelms him, and their relationship takes a new, intimate turn.