Three years into their marriage, Eri and Kiyoshi still get along, but their sex life has steadily faded. Unable to ask her sexually indifferent husband for more, Eri secretly satisfies herself. One day, Kiyoshi's older brother Tsuyoshi catches her masturbating. He reassures the embarrassed Eri that there is nothing shameful about it while pressuring her into sex. Overcome by curiosity and his forceful advances, she gradually exposes every desire she has kept hidden.