At age 40, career woman Yumiko Izumi, seeking to fill the emptiness in her life, has secretly registered with a mistress bank under the alias "Yuuko," becoming a nightly companion for various men. Successful in her professional life, she now lives for pleasure in her private affairs. Her path crosses with Ishihara, a client company president, who has discovered his wife's infidelity and devised a plan for revenge—hiring a woman from the mistress bank to perform sex in front of his wife as retribution. Unbeknownst to all, the woman summoned for this act is Yumiko herself. As longing and desire intertwine, Yumiko abandons her inhibitions and reveals her true self. In doing so, she steps into an entirely new realm of existence.