Thousands of years ago, in the dark ages, demons ravaged towns and fought for territory. In the chaotic times, the saints sacrificed their lives for magic, sealing demons in books filled with sacred texts. As time passes, the devil's body is eaten up by magic. The demon did not die, and the dark force hidden in the demon gradually eroded the seal of the holy letters, which became a banned book. It constantly called upon the powerful human beings in the world, and made them containers to bring the Dark Age back to the mainland.