Having formerly reigned over Japan's criminal underworld, the Koyomi clan is now in disarray. With his family decimated, Kashitarou Koyomi is disconsolate and abandoned. Enduring the animosity and anger of others, he is offered the services of a caregiver and mentor named "Nazuna." Gazing determinedly at him, she declares, "My goal is to transform you into a formidable antagonist!"