Henkyougurashi no Maou, Tensei shite Saikyou no Majutsushi ni Naru

There was a mage called "The Lone Demon King" at the frontier. He was just a creature that never grew old, but he was loved by the villagers as something of a guardian deity. However, he was destroyed by a magic organization that sees his existence as dangerous. 200 years later, he is reincarnated a