Gekido

Gekido (激怒, Gekido; Rage) is a young mage and the adopted son of the Wizard Saint Julie Tsezeer. Gekido has trained under Julie from a young age, holding no memories of his birth-parents whatsoever. Julie has told him they were former clients of hers that she had been hired to guard as they traveled through an especially dangerous area, but things suddenly went array in the middle of the trip and Julie was only able to save Gekido. This however is pure fiction that Julie conceived to hide Gekido's true past from him. In truth he is actually spawn of the Black Mage Zeref that was created centuries ago. He wrought great destruction on the land, but was eventually sealed away in one of the Books of Zeref. For two centuries he lay undisturbed within the book, and he would've remained that way had he not been discovered by a Dark Mage. The mage attempted to free him and make Gekido her personal soldier, but once he was unbound Gekido turned on her. The Demon quickly caused an uproar in the surrounding area, slaughtering dozens of civilians until he was abruptly stopped by Julie. The two powerful forces fought, but Julie managed to seal him once again, this time in the body of a boy he'd killed. In this form Gekido has no memory of being a Demon, and much of his power has become dormant within him. He does however occasionally see glimpses of his actions as a Demon in the form of vivid nightmares, though of course he hasn't the slightest idea the monster in his dreams is himself.