Hametsu no Madou Ou to Golem no Ban Kisaki

In a world of swords and sorcery, a ritual summons the “sorcerer king” who will bring ruin—but all it coughs up is an ordinary boy from Earth. Stripped of his memories but endowed with unbelievable power, our protagonist isn’t keen on destroying the world. Fortunately, tinkering with his newfound power results in the creation of an intimidating partner to keep him safe!

(source: Seven Seas Entertainment)