Excerpts from Atheian Sources
From The Gentlemen's Guide to Realms
There are three realms, which are also called planes, that exist, and are known to exist. These would be Atheus, the Afterlife, and Congeria. Each of these are inaccesible to each other, except for two key exceptions. The first of these exceptions are when someone in Atheus dies. The dead's soul then goes to the Afterlife. Experiments done by leading Sciremagi have not yet discovered how the soul travels there. The second is with demons being summoned from Congeria to Atheus.
These realms are inherently separate, and do not exist on the same level. In short, they are different realities, separated by a gulf of nothingness. Still, most of the knowledge we have for these different realms is hypothetical only, as no way of travel between any two planes have been invented (naturally, this statement does not take dying and you soul going to the Afterlife into account).
From Demon Work Force: A Moral Choice?
For thousands of years, mankind has been summoning demons, and using those demons to do various tasks. As the typical demon is born with extraordinary magical talent, and is able to shape-shift near to will (further abilities depends on the type of demon), they make an excellent work force, and have helped with various endeavors of man. Examples include the Trirexian Palace, the Lost City of Mare, and the entire Elto-Drenar war. The demon can be used as a potent weapon or a valuable architect, all depending on what instructions you give.
Still, there are examples strewn throughout history of demons succeeding in rebelling against human summoners. If the person summoning them makes an error- even a small one- a demon can throw off their bonds and kill the summoner. The killing of the person who called them to Atheus frees them, and they return to their home plane of Congeria.
If one examines demon motive for the killing of their master, one finds they have excellent reason for doing so. Demons are treated as little more than slaves, corralled into staying in a hostile world they are not used to or born in, and frequently abused. This abuse mainly comes from a variety of spells used against demons as one would a whip. Demonologists, or someone who studies demons, and may or may not be a wizard and have the ability to summon a demon, have found that staying in Atheus for prolonged periods reduces a demon's strength and vitality.
From Demonology: On How to Control Your Demon
A demon is not a pet; a demon is a very dangerous killing machine barely controlled by whatever magical bindings you trap it with. They are devious creatures, and are constantly striving to destroy you. Never underestimate them, never let the guard down, for even the lowliest of imp can, if given but a single chance, destroy you.
Perhaps an explanation of what a demon actually is will illustrate my point. The demon originate in Congeria, their native realm, and are born of a seething mass of chaos. Indeed, the word “Congeria” itself meens, in the Old Tongue, Chaos. And when they come here, they bring naught but death. A demon is a killing machine, equipped by Mother Nature herself with a variety of deadly enhancements. They can shape-shift at will, and can freely change from a 100 pound bear to a highly poisonous snake. They have a variety of demonic magics that are second-nature to them, and cast spells that have destroyed an entire city. They have a true form that they hide, and the sight of which would leave you mentally and emotionally scarred for life.
No, the demon is a constant, wily, threat. The demon summoners who die are the ones who forget that fact.
From Jacob Latris' Journal
The teleportation to Congeria was a rough, draining experience. I had flashes of my own mortality as I traveled through the void. I arrived in a desolate field, devoid of life. The scene was harsh, and an unnatural light was shed. The clouds above are a deep, deep red, and very dense, but still, I had a feeling that they did not hide a sun that shed the light I saw the landscape with.
I saw not the demons who supposedly inhabit this place. Could it be possible that we do not in fact summon the demons, but create them through the process of the spell? No, no, that is absurd. It contradicts all I have discovered in my path to find Vengeance. A slippery prey, to be sure, but I am more than a match for it.
I then immediately set to work in that place. First, the mundane work, fit for a simple commoner. If only I had an assistant for those tasks beneath me. But then I did not, and so then I started work on a map. As such, I took stock of the mountainous structure before me, and the lake of, I believe, Chaos surrounding it. I made a rough sketch of the place, to serve as my guide in that place.
From Jacob Latris' notes
The demons are vacant in Congeria. I have explored this entire place, except for the depths of the Chaos Lake, and the island in the bay, and have yet to see a single demon. Three theories come to mind: the first is the spells that summon demons from here instead create a demon; the second is that they are in the depths of the Lake; the third is that they hide whenever I approach in such a manner that I cannot detect them. The first two seem to be far more likely than the latter.
Twin Peaks are crucial part of landscape- further testing is required. Hovering between them, at the tips, is what appears to be a green fire, standing in contrast to the mostly red terrain of Congeria. Experimentation with this green fire has revealed multiple possibilities of what it is, however, one of those strikes me as the most likely: The green fire is, in actuality, the source of magic.
Tests I've conducted on the effects of the light on objects has revealed that the constant exposure to the “pure” magic shed by the green fire adds lingering effects on the body. As it would be imprudent to conduct tests on my own body, I have tested the effects on a variety of animal subjects, most notably pigs. In most cases, the pig subjected to the green light in Congeria mutated in a variety of ways. The most notable was bodily changes. The addition of horns, tails, organs, etc., were noted. Enlargement or change of existing body parts were common, and occurred on all the test subjects.
Some shorter lifespan creatures, such as a dragonfly I brought, died far quicker than can be expected from the species. The cause is unknown.
The planes are all intertwined and connected in a form of trade. In short, each plane (Atheus, the Afterlife, and Congeria) all export one product to a certain plane. Atheus exports the dead's souls to the Afterlife. Congeria exports demons to Atheus (unwillingly on the demon's part, I might add). A great many sciremagi in Atheus have postulated that the Afterlife sends something to Congeria, though the identity of that something could only be guessed at. That something was processed souls.
The Afterlife, somehow (no one in Atheus, including the planar explorer Jacob Latris, has stepped foot in the place to find out) changes, adapts souls from Atheus, which are sent to Congeria. Those souls, transported by the pure magic that is the green fire at the top of the Twin Peaks, are at first invisible to the naked eye, nor any of the other senses after they first exit the fire-portal. But the magical “radiation” of the Green Fire that Jacob Latris' noticed slowly changes those souls, and converts them into demons. The demon is a creature of magic, with an identity and life born of the soul from Atheus.
It should be noted that not all souls from Atheus go through Processing in the Afterlife and become demons. Some souls simply don't have it in them to be demonified.
After the Green Fire's light finishes converting a soul into a demon, the light starts to pain it. Perhaps pain is the wrong word- for that is the human's nerve response to something that seemingly inflicts bodily harm. It is the demon's innate sense that they have bathes in the Green Fire's light for too long, and now it must submerge itself in the Chaos Lake.
The Lake itself is composed, purely, of demonic essence. Chaos in its purity. For the demons, as well as magic, are things of chaos shrouded in order when they go to Atheus to serve a wizard's whims. The Lake, composed of demons in this form, protects and shields itself from the effects of the Green Fire. This protection is necessary, for if a demon stays too long in its light, it too may perish.
When a demon is summoned to Atheus, the time spent outside of the chaos that is Congeria weakens it, steals from it the magic that made it a demon in the first place. They become weak, less-abled servants, whose mighty command on magic (for a demon is magic personified, though the peoples of Atheus don't know that yet) shrivels and weakens. Which is why wizards who summon demons will dismiss the demon back to Congeria. There, the demon will, instead of returning to the Chaos Lake, bathe itself in the Green Fire's light and return its energies to normal, before returning to the Lake to protect itself from the Fire.