Aimu Kuroki, a slender married woman whose husband is away on a long-term work assignment, stays behind at home with her father-in-law. Filled with loneliness, she copes by masturbating daily. One day, her father-in-law accidentally witnesses her in the act. Seeing her longing and sorrow, he sympathizes with her unfulfilled desires and offers to satisfy her. Initially resistant, Aimu gradually gives in, drawn to the relentless passion she experiences with him. Despite feeling guilty toward her husband, she begins to surrender herself completely to her father-in-law, seeking the unique pleasure she cannot find elsewhere.