Demon King: "I hear that revenge and comeuppance stories have become popular lately. So, would you mind letting me join your hero party and then kicking me out?" Hero: "Get out of here!"

(The Demon King Returns Chronicle, First Edition) The Demon King was dead. The Hero had killed him. But alas. The Demon King was a being that repeated infinite reincarnation by using corpses as vessels. As long as humanity existed, the Demon King would continue to revive endlessly. Humanity had no means to destroy the Demon King until two hundred years later, when the Demon King's true body would revive. Fearing the Demon King's reincarnation into a pillar of the state, the Church forbade the Hero from killing the Demon King recklessly. And so they decided to confine the Hero—humanity's trump card—in an ancient castle deep in the mountains, keeping him there until his death. Today as well, the Demon King draws near to that Hero's location. ...For the sake of killing time.