Kenja no Mago

A Japanese office worker dies and is reborn in a world of magic as Shin Wolford, where legendary mage Merlin adopts him and raises him far from society. Shin grows into an extraordinary talent, combining magical training with knowledge retained from his former life to create techniques that seem impossible even to experienced sorcerers.

When Shin turns fifteen, Merlin realizes one major part of his education was forgotten: the boy knows almost nothing about social customs, money, or what ordinary people consider a reasonable amount of power. He enters a magic academy to learn alongside people his age and becomes famous almost immediately. Between new friendships and threats involving humans transformed into demons, Shin must learn that overwhelming strength means little if he does not understand the world he wants to protect.