Due to work reasons, the brother-in-law has to live with his younger brother and his wife for a while. Although the younger brother and his wife live happily together, Yukino is frustrated and lonely because her husband is not trying to have children. The brother-in-law understands how she feels and approaches Yukino to take the place of his useless brother. Yukino refuses to be unfaithful, but her brother-in-law's repeated cunnilingus makes her unable to suppress the pleasure and they end up having a relationship. Captivated by his gentle and passionate caresses, Yukino ends up seducing her brother-in-law and becoming immersed in an unfaithful relationship.