Entering his second year of failing to get into college, son Shigeru is overwhelmed with daily studying and growing stress. Seeing his condition, mother Natsuko grows concerned, and one night she discovers him masturbating himself to sleep. Though initially resistant, Shigeru's earnest dedication to his studies moves Natsuko, and she eventually gives in to him physically. From then on, their secret affair continues. When Natsuko's private tutor Nachi learns the truth, she confesses her own frustration—suffering from a sexless marriage and resorting to nightly masturbation. Driven by her own pent-up desires, Nachi makes a bold proposition to Natsuko.