Ikumi Shiramine is a serious and plain office worker who works at the same company as her earnest but self-centered husband. Growing tired of his egotistical nature, she begins to feel lonely and neglected. Under the guise of business entertainment, he frequently visits clubs filled with women, submitting fake receipts to satisfy his desires. Witnessing his behavior, Ikumi silently harbors resentment. Though she appears innocent and diligent, her mature, voluptuous body betrays her restraint—night after night, she indulges in secret masturbation during late overtime. One day, her boss, Mr. Ozawa, accidentally discovers her in the act. Using this lewd act as grounds for disciplinary action, he transfers her to become his personal secretary—effectively making her his mistress. This marks the beginning of a new life for Ikumi, one filled with illicit pleasure and carnal indulgence under Ozawa's control.