Natsuko is troubled by her second-year son, Shigeru. One night, unable to endure his daily routine of studying, Shigeru sneaks into Natsuko's room after satisfying himself and tries to have sex with her. Initially, she resists, but seeing his sincere plea 'I'll study hard,' she ends up giving in. The tutor, Nachi, finds out about this habit and complains that she too is sexless with her husband and spends every night masturbating. However, Nachi makes an outrageous proposal to Natsuko to satisfy her own desires...
