A Different kind of Devil Dungeon
Devil Dungeons were a very unique occurance in the world.
Maybe it was the nature of devils, or it was the morningstar in his ever enlightenment as he set the criteria for their kind.
Devils were made to be the bane of Demons and as such, were responsible for the maintainace of peace between the Royal demon families, occupying a royal position themselves.
However, that was only on the condition that their ruler was still alive. Without the control of the power of the morningstar himself, Devils were plain beings of chaos.
But even in this annoying chaotic state, capable of perverting the world around them with their chaos magic, they were still able to carve for themselves a unique eco system that functioned based on power level supported by even the cosmic laws.
Supported so much that those demons of a higher power level could not enter the domain of the highest devil within the Dungeon.