They call it evil energy. Under the right circumstances, energy can be molded, tainted, and harvested for entirely different purposes, like controlling beasts. Demons like the Honuyál have mastered this, along with their brethren. When the energy of the Soul Realm was tampered with, it had devastating consequences. This is energy that shouldn't be harvested by anyone, but most specifically the Gods. This energy consumes everything, and is responsible for the current state of the Soul Realm.