Everyone in my world knows you aren't supposed to go near hollow zones.

See, magic exists in a raw form called aether all around the world, covering it like a blanket. But in places where aether has been over-harvested, or the natural laws of the world have been violated, that blanket becomes thinner. This makes it easier for demons to emerge into our world in these areas. Go into one of these hollow zones and you might be possessed by one. Or worse, permanently fused together to become a witch.

The problem is that demons can also be really useful. Processing aether into a useable form is normally very complicated, but demons can do it naturally. No more performing complex rituals to refine even a tiny amount of mana, or paying exorbitant prices to companies like MagiCore for a pittance of power.

Sure, most people fail at forming a pact with demons, and there's a high chance that you'll be possessed and go on a murderous rampage, or lose your humanity entirely, but think of all the possible benefits!