The primal demons...
When the gods first made contact with the humans, some of them found attraction towards the beauties of a small village in the plains. As they first created the children of the gods, a bed of flowers had bear witness to such contamination of their blood. Seen as omens of destruction, the first children of the gods were prosecuted and hunted down.
Due to the violence they lived through, they turned into dark entities that carried the power of the gods. They were the primal demons, ancestors of all the demonkind.
It had been long rumored that the Abyss served as the prison of the primal demons. Now, the news of a primal demon breaking out of the Abyss proliferated. However, due to the lack of physical evidence of its return, no one believed in it.