The cosmos is built on dualism. And endless shifting between Order and Chaos. Mysterious powers from beyond the veil of space and time influencing reality like a dark force creating rippling echoes throughout the universe.
Central to the dualism, is the ability to tap into these forces, and channel its power to endless possibilities. The nature of these powers are known, mapped in lore, but to say there is any being that truly knows its limits, or even its purpose, is to profess foolishness.
The first beings of Myrth penned what they called the Great Myth of Creation and it lends itself well to explaining the dualisms of reality.
Aevum was a two faced god. One side was without features or expression: the embodiment of his laws. And the Laws he infused into his creation. The other was dynamic and ever changing: the embodiment of chaos and ultimate potential. The two sides on which the cosmology is based are the two extremes of Order and Chaos.
Good and Evil has no influence in the way the cosmos is structured. Morality has no meaning in its form. Creation has rules, yes, defined by the ultimate expression of Law. But it also has unending potential, defined by the ultimate expression of Change.
In the Realms of Aevum, the plains of existence overlap with each other through gateways. These gateways manifest as Sources of Power on Myrth, by which beings can travel between them through the Myst.
The material realm is known as Myrth. It is a stable realm with a relatively small amount of Myst influence compared to some of the other realms. It is therefore a realm of infinite possibility, in perfect balance between Order and Chaos. In close proximity to Myrth are the realms of Aegis and Nox, manifesting as the two moons of Myrth.
Aegis is a realm of order and law. On it resides many cities of outsiders who are in a constant state of flux against the creatures of Nox. Nox is in turn a realm of chaos and entropy, standing as opposition against the creatures of Aegis. Good and evil plays no role in the origins of these realms.
Beneath the material realm is a place contained primarily by the seeping through of the Myst, called Tartarus. It is part of Myrth, Aegis, Nox and the Myst, linking these three realms, and the primary reason why they are able to influence each other so greatly. Beings from each realm can freely cross over into the Nether, but cannot enter any realm beyond their own without aid from that side. Across the eons the Nether became a battleground between Aegis and Nox, in order to increase their power over Myrth and the material realm.