Amanattou

Summoned to another world to defeat the demon king, Satou Sousuke, 18 years old and only finished elementary school, is brought back to his world after several years had passed. While unable to find employment anywhere and living off a part-time job, Sousuke encounters a battle between a magician and a demon he thought didn't exist on earth! He easily defeated the demon, so being marked for his power he's involved in Demon subjugation!?