Mudzan Kibutsuji is the progenitor of all demons and their king. A millennium ago, during the Heian era, Mudzan was turned into a demon as a result of experimental treatment for his incurable disease. Since then, his goal has been to live without fear of death and become truly eternal. For twelve centuries, Mudzan has been searching for and developing the medicine "Blue Spider Lily". The first medicine of the same name made Mudzan an immortal being who is not susceptible to diseases. It also easily tolerates poison made from wisteria. Later, Mudzan decides to create a group of the twelve most powerful demons, nicknaming them the "Twelve Demonic Moons" for his potential protection and combining them with two goals: to remove all demon hunters, as well as to find his cherished medicine.