Exhausted both physically and mentally from caring for her father-in-law, 'Natsume' one day finds her attention captured by his sudden erection, her heart racing at its impressive size. His manhood, embodying the masculinity of a Showa-era man, leaves a deep impression on her mind. An insatiable desire begins to grow—one that masturbation can no longer satisfy—and her longing to be close to her father-in-law intensifies each day. Their relationship gradually transcends mere caregiving, evolving into the beginning of a forbidden passion.