Set during the Meiji era, Satoko Kirigaya is a noblewoman with a weak heart who dreams of marrying for the sake of her family. Her life changes when she is targeted by assassins and rescued by Shinpei Goto, a dangerous killer with an obsessive personality. To survive, Satoko impulsively proposes marriage to him, expecting it to be a lie. However, Shinpei takes her proposal seriously and becomes fiercely devoted to her. The story blends romance, suspense, and danger as the two grow closer despite the violent world around them.