"I never thought that I, an ordinary housewife, would end up in such a relationship with my younger brother at this age..." Ai Kano (Ayaka Kurahashi), a sister in her late 30s with two children, takes on the job of doing housework for her younger brother Takumi, a single aristocrat in his 30s, to help with the household expenses. However, Takumi, who had unknowingly awakened to a mature woman fetish, harbors a secret lust for Ayaka... Takumi, who ended up in a relationship with her on a whim while drunk, continues to seek her out afterwards and proposes a detached relationship. While saying "for the sake of the household expenses," Ayaka's body is overwhelmed with a guilty pleasure as she experiences the pleasure of adultery for the first time...