Fiction:The Firmament/Corruptus

Corruptus is the abode of the demon lord Shurin Rodin, the lord of fear and nightmares.

Description
Corruptus is a dark and cavernous lair where the most terrible nightmares of mortals are made manifest. Shurin Rodin rests at the deepest reaches of Corruptus, watching and studying what causes the most fear in mortals so that he may devise the most traumatic of nightmares. Every time Shurin Rodin kills a powerful opponent, such as a nascent demon lord rival, he unmakes their souls into their most primal fears and uses them to empower Corruptus, turning it more and more evil each time.

Inhabitants
Demons are continuously born from the fears of mortals, and most who emerge from within Corruptus hold their allegiance to Shurin Rodin. When mortals have night terrors, particularly terrible creatures are spawned in the realm, which Shurin Rodin either uses against his demon lord rivals or attempts to send to the Material Plane to cause havoc.