The Burnt of Holy Magic (2)
There was only one foolproof way to destroy a demon, especially when it come to an aristocrat ones. The higher their rank was, the more difficult it would be to eliminate them. Even defeating their minions would proof to be a challenging task. No amount of magic or element could significantly hurt higher demons besides the completely opposite attribute to their nature, and that was holy magic.
Light against their natural darkness. Even the previously amateur Argan knew that he was weak against white magic when he had first spawned in Zarronium. It was like a common sense that was ingrained in their subconsciousness as a dark creature.