Henkyou-gurashi no Maou, Tensei Shite Saikyou no Majutsushi ni Naru

There was once a mage called The Lone Demon King on the frontier. He was just a creature that never grew old, but was also 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 as the second son of an aristocrat and obtains the strongest magic power.