INTRODUCTION
In our everyday lives few of us recognize the various planes of existence that permeate our own world. Sometimes these planes lay parallel to our own, separated by but a thin veil. Other times we exist in several planes at once but do not sense our multiple influences. And still other times we exist in but one world, but influence other planes without knowing it. It sounds confusing, but a few examples will make it all clear.
ORIGINS
The last case, of living in one world, but influencing other planes without knowing it is by far the most common situation. In order to keep the examples simple we will first focus on one plane, in this case the Astral Plane, and use its principles to help explain all the other planes.
Before delving further into this topic it may be helpful if you are fully conversant in the differences between (and origins of) Divine Magic and the Weave (or Mage Magic). In the same way that merely "being" creates a force we call the Weave which Mages tap into, there is some spill over of spiritual energy which all sentient beings experience. Unlike the consciously directed spiritual energy (by prayer or wishing for something to happen) that creates Divine Magic potential, there has always been some unconscious spiritual energy. Every good act creates some energy of one sort; every evil act creates energy of another. In total, since the beginning of life there has existed a great sea of raw energy known as the Astral Plane.
The Astral Plane really exists. One can visit and travel there. It is the home of most of the Gods. There they abide and complete the Worshipper-God-Priest continuum. And their realm is supported in this plane of undirected spiritual energy just as earth and wood and light support ours.
The Astral Plane existed before there were Gods in the same way that sentience existed before there were Gods. All living creatures have spiritual energy, and long before Elves or Dragons existed there had been created the universe-spanning Astral Plane. And in that rich realm life found a foothold: life native to that realm. We generally call them spirits, but not in the sense of "spirits of the dead", rather in the sense that they live and can be destroyed in a realm of spiritual energy.
NATIVES OF THE PLANES
The different sorts of spiritual energy (good or evil and all the ranges in between) created a limitless realm of spiritual space. Life there arose naturally, eating and drinking and breathing the spiritual energy as we mortals eat food, drink mead and breathe air. These native forms include tanar'ri, baatezu, devas and yugoloths, to name but a few. Now whether an exceptional spirit gave rise to the intelligent mortal races we know, or the races through their desires gave rise to exceptional spirits (now called Gods), is a debate resolved only in the origin stories of every species. But whatever the case, a select few of these native spirits are now linked directly to worshippers – having grown in power through consciously directed spiritual energy – and are now known as Gods.
These native spirits to the Astral Plane have changed over time. Some grew to hate others and fight with them. Some have aligned with specific Gods and choose (or have been forced) to serve and help them. The Gods themselves may very well treat these wondrous native beings the same way as we humans treat horses, dogs or elephants in our world. This analogy fits, for just as these spirits are usually far greater and more powerful than most beings on Seteria, so too are the Gods far greater and more powerful than the native spirits.
AVATARS, DEMNAI, ANGHAI
The Gods are nothing if not creative. Most have families, other Gods or members of a pantheon to which they belong. Many are credited with creating life, worlds and the entire universe. Their divine brethren are sometimes said to have arisen from the blood or power of the pantheon's founding God, or in some cases have attracted enough worshipping power to become Gods in their own right.
The Gods have also created partners and helpmates, or guided and entrusted others to help them. At the lowest level, various Gods have enlisted the help of various native Astral creatures. For example, many good-aligned Gods have devoted allies and companions in the form of aasimon: Devas, Planetars and Solars for example.
At the next level of power and closeness to the Gods are the Avatars. These beings are a direct extension of the God's power. They are directly associated with one God or another, effectively created by the God splitting off a small portion of their divine and virtually unlimited power. They are unique to that God. They share some of the God's power and can act directly on their behalf. And while not the most powerful helpmate a God can have, they are usually considered the most intimate being that any God will know aside from other deities.
The mightiest of helpers to the Gods are unique to the Andronese Mythos, and are known as the Anghai and the Demnai. Though not quite Gods themselves, they are like avatars in their relationship to their God, and virtually unrivalled in power.
OTHER PLANES
The preceding passages speak of the Astral plane as an example for all others. In the simplest terms, the other planes consist of the Ethereal plane and alternate prime material planes.
The Ethereal plane is where the essence of all material things may be found. In much the same way as spiritual energy is the foundation of the Astral plane, in the Ethereal plane one may travel to the foundations of Earth, Air, Water and Fire, and all the combinations of those elements.
Thus, by passing through the Ethereal plane one may reach the elemental plane of Earth. Similar to the natives that are found in Astral plane, there are natives on each of the elemental planes. There one may find Xorn or Crysmals to name but two natives. On the other elemental planes one might find Nereids, Magmen and so forth.
In the same way, there are alternative prime material planes. These are realms seemingly similar to our own. There one might find elves, but who are barbaric and live like animals. Or in another realm worlds that flat and have suns which go round them. Or worlds which know virtually nothing of magic nor the Gods.