Over a century passed without a Sperado heir capable of controlling the shadows until Marquis Sperado sought to enhance his eldest daughter's feeble abilities by sacrificing his second-born, Leslie. Leslie, intended solely to serve her sister, was saved from certain death by unknown entities, awakening a previously untapped shadow magic stronger than her sister's. Enraged by her family's abuses and practices, Leslie chooses to sever ties with them and turns to the "Monstrous Duke," Acela Benkan Salvatore, to broker a deal. In exchange for a normal life until adulthood with the Salvatores, Leslie pledges herself as a "Dark Saint." Focused on escaping the Sperados' grasp and pursuing happiness, Leslie will stop at nothing to secure Salvatore protection.