Tsuyuri was attacked by an evil demon when she was a child and has an ugly claw mark on her chest. After losing her parents, she was taken in by her cousin and forced to work day and night in exchange for her brother's medical expenses. Tsuyuri is mistreated as the “handmaiden of an evil demon,” but she perseveres for the sake of her younger brother. But when she discovers the cruel truth, a black wolf appears. The beast transformed into a beautiful man. “This is a contract. The contractual marriage of mutual interest began with the words, I want you as my bride." But what is the true meaning of his sweet and doting love for her...?!