THE NEXUS
The Multiverse is composed of the infinite number of realities, each of them representing a possible state of the world as we know it. If you were to toss a coin there exists a reality where the coin fell with heads up, another where coin fell with heads down, and yet another where a lighting bolt blasted the coin out of existence after you threw it. However all these realities have a single variable in common: Time. Many of the realities intersect and where the barriers between them are thin enough, those with the proper ability may step through into another reality thus traveling through the Multiverse as if it were a infinite jig-saw puzzle.
There however exists what is essentially the 'space' outside of all the realities of the Multiverse. It is the realm of chaos and entropy, of raw stuff of Multiverse yet unshaped into any form by forces of Order. And unlike all other planes of Multiverse it posses a unique property: It borders on ALL the infinite reality planes and thus is known simply as the Nexus. The struggle between Order of Multiverse and Chaos of Nexus is eternal, and the boundaries that separate these two antithesis are strong enough to prevent any direct travel between these opposite poles of existence.
The Nexus is an alien realm and beyond understanding to most minds shaped by Order. However it is not uninhabited. Denizens of Nexus range from insentient forces of raw chaos to Demons possessing the power of gods, and they are ever driven in their lust to corrupt Order and return its dominion to its primal state of entropy.
Physical travel across the boundaries between the Nexus and rest of the Multiverse is not possible except for the brief time once every 10th millennium when the triad of Aabahran's moons creates a gateway into the Nexus. Beacuse of this the forces of Chaos have long used possession of mortal shells as an alternative means of affecting the Dominion of Order known otherwise as the Multiverse.
CHAOS DEMONS
Faced with the impossibility of planar travel into the realms of Order, the forces of Chaos found creative ways of bending the rules of the Multiverse in order to enter it. A mortal shell may be possessed by the essence and "mind" of a powerful enough Chaos spawn, thus allowing a portion of its power and abilities to be present in the realms of Order. Once established the link is permanent unless somehow broken, transforming the mortal shell into what is known as a Demon. Possessing no speech yet potent intellect and a form of telepathy, these great beasts are strong and dangerous. If the mortal shell was not a willing host of the Chaos spawn, it is called a Torment though the physical attributes of the resulting demonic form remain the same.
