Kouhi Mayumi is perceived as a housewife, but her true identity is Mistress Blue, a member of the Mistress Ladies. She has been entrusted with a transformation brooch to protect the world from an evil organization that operates in the shadows. However, her secret is discovered by her husband's boss, Goro Sumiya, who has been planning to take advantage of her for some time. He steals her transformation item and demands that she engage in infidelity with him in exchange for its return.