~the musings of an amateur cosmologist~
When one is creating a universe, one must of course choose an organizing principle for it.
The circle of life, the cycle of reincarnation, the passing of duties from ancestor to descendant. Though it differs in specifics amongst the many species who dwell within, it is this process that unites them all: beings which are mortal are made of the elements of the earth. And all that is built of the earth will, someday, crash down again.
(Those who created the world, of course, are different: creatures of will and vapor, metaphor and song; the quintessence that forms their flesh does not decay, and so they are eternal. But that is not -- directly speaking -- my field of interest.)
Because this cycle of life and death is so fundamental to all the physical life within, we must therefore assume that the structure of the world is organized such that it supports this cycle directly.
And so our observations would appear to suggest. Not one, but two of the exterior planes are devoted to this cycle: Letheon and Netheos, which contain the mechanisms of rebirth and unlife, and thereby keep the process of rebirth operating for Creation's living beings.
This all seems eminently sensible on its face, but it begins to raise rather curious questions as you investigate it further. There are six planes of existence which touch upon Meru; why does only Netheos impinge itself through overlapping contact points created via sympathetic activity? Why is the process of dying riddled with uncertainties and differing results? Something seems to be off.
Some careful investigation has pointed towards the cause -- but first, a little background. Each of the planes lies in the mutable medium that we refer to as the "Wyld," and is connected to its neighbors by pathways of partial stability through this medium, similar (in kind, but not in scope) to those created by rote action at the borders of Meru. It is through these passageways that the Path of Stars moves, and it is at the natural points of equilibrium midway between these planes that the membranes form: the points of transition at which the regional influence of one plane transitions into that of the other.
These membranes have an existence of their own and their own unique properties. Each of them can be used to bring the two planes into temporary conjunction through the application of sufficient ritual sympathy (although in experiments, there is no quantity of squirrels that can be assembled in one place that will produce a spontaneous portal to Elysion); however, these are indeed temporary in that they naturally fade as the sympathetic conditions are eliminated.
With Netheos (and, it appears, Letheon -- though this is much less common) this natural healing process has broken: sympathetic events create temporary holes that are wrenched open and stay that way, destabilizing the existence of both worlds by allowing the unencumbered passage of differently-aspected Essence. It was in investigating this specific mystery that I formulated my theory.
The membranes of opposing (and therefore, thematically linked) planes tie into one another, and the tied membranes of Letheon and Netheos to Meru are special: unlike the other inner planes, these are spiritual planes, and their passageways are used regularly by the spirits of the recently departed. Other documents within the library point to this membrane having been known as the Shroud, and I will refer to it by this name.
When the Primordials created the universe, they did not write the possibility of their own deaths into it. When the first of them were slain, it seems that their vast spiritual bulk -- normally distributed elaborately throughout the structure of the universe -- was forced simultaneously through the channel, providing enough powerful, Essential motive force to punch huge holes directly in the membrane between death and life. Thus, where once the forces were carefully balanced, now the entire process is skewed: dead bodies rise up of their own accord, souls are reborn to the wrong bodies, and the temporary places of overlap fester into Shadowlands instead of closing of their own accord.
The process of repairing this damage, unfortunately, is far beyond the level of my current understanding to suggest. However, the benefits are worth noting. Scraps of older text seem to point to the unusual properties of this membrane, at the time when it was whole. A ritualized passage between the worlds seemed to be able to create effects mirroring the regular passage of souls between them -- a passage to Netheos bringing about the peaceful ending of something, a trip to Letheon aiding in the rebirth of something long-since departed. As long as the Shroud remains tattered and broken, however, it seems unlikely that any such effects could be achieved.
This is an area worthy of further study! I intend to perform followup experiments based on the other instances of physical/spiritual planar membranes: the connections of Wasirru and Elysion to Yu-Shan, and of Xara and Atomnos to Malfeas. I will also be doing further examinations on what I have termed the "Brightland" that has emerged in the Eastern forests, in order to more fully understand its qualities. Hopefully with greater work, I, Uuresh Seven-Tamed, will make the breakthrough needed to solve this matter once and for all.
-- text from the Sublime Refuge of Unquiet Thought