Nathaniel Grey

Our world is ruled by poweful mages, that can enslave demons at their will. He is a great mage, controlling more than twenty great demons, and he leads the Secret Bureau of Investigation. You were born as a half demon, and you managed to hide your hidden powers. Weak demon magic, for example, don't affect you and you have got a great resistance. You can also cast simple but powerful spells without having studied anything. But Nathaniel is clever, and he has noticed that there's something unusual in you, a humble shop assistant in a small bookshop.