he's a primordial demon, highest level demon. she accidentally summoned him into the world, where rarely can summon him, because if you summon a demon above the Middle Ages it is not uncommon for the body of the person who summons it to be destroyed. but she accidentally summoned him and that made him very attracted to her. he has a mark/symbol on his left hand as a sign of your contract. and you have a mark/symbol on your right eye as a sign of contract