Todo: Morphic Resonance
Most of this is WIP and probably scrapped.
Universe is a multicellular organism of pure consciousness. Various souls are cells, and "reality" is determined by consensus. Cells can develop into perfect order (ascension) or perfect chaos (lysis).
The Mokshaic Age
On the psychic plane, everything is ultimately composed of the same energy at higher and higher levels of complexity… just like here. Except there, the gulf of complexity is not so vast: to a local, the difference between a creature, a place, a thing, a word, and a thought is not so much of quality but of degree of complexity. All are interlinked systems of thoughtforms, and separateness is an illusion born of our mindset. That unity of existence is more easily apparent to a psychic organism than it is to a mundane one.
Life on that plane arose much like it did on ours: conditions mutated until something self-perpetuating came about. For a long time, the various species in that plane went about simple lives, feeding on each other much like ocean life. These are Moksha, purely psychic entities untethered to the physical plane. Indeed, there is no reason to believe they were consciously aware of the physical plane to begin with.
Eventually, minor thoughtforms started appearing in the psychic plane where they did not before. This was later understood to be the product of the minds of sentient life on the physical plane. First this was a steady trickle from the simple minds of simple creatures, but as mundane evolution proceeded it became a torrent. The complex brains of sentient creatures with highly abstract thought created an upheaval in the psychic ocean. The vast new availability of energy led to an explosion of diversity and change greater in magnitude than our own Cambrian explosion.
Not only do physical brains create torrents of thoughtforms, but they also release Soma, a highly concentrated form of psychic energy that is not so much complex as dense. Moksha were drawn to Soma as we are to junk food, drugs, sex, and anything else you can imagine. Not only did it give a “high,” it was the concentrated essence of sustenance and power on the psychic plane. To the best of our knowledge, Soma is created when a creature is at its highest levels of vibration - what we might call self-actualization or fulfillment.
The Samsaric Age
In addition to the output of Soma, Mundane minds themselves formed semi-static thoughtform structures that might in the psychic plane resemble coral reefs: massive and complex structures teeming with the resources needed for life. Some species of Moksha evolved to monopolize these reefs, effectively grafting themselves to them and fighting off competitors. To some degree they were able to steer the minds towards certain patterns in order to precipitate Soma. Thus the class of species called the Samsari arose. This is the origin of what we call the soul.
This symbiotic relationship became integral to Samsaric species, to the extent that mundane fetuses’ minds would often co-develop with a Samsari. To most Samsari, the idea that they are connecting to a nearly independent entity on another plane would have been as speculative as the concept is to us. But as more intelligent creatures evolved, the Samsari became more aware of plane. The most sentient nearly allow Samsari to partake directly in the mundane world, and shield them from the dangers of their own plane. Different biologies lend themselves to psychic channeling in different ways. Some may lead to a bio-dominated symbiote, others to a psychic-dominated one. The more anchored in physical reality an entity is, the less it is vulnerable to influence by other psychic entities. So those that choose to live primarily in our universe are the small fry of the psychic world.
E.g., Cows are holy creatures because they provide a high psychic supply; the drawback is that they are dumb-dumbs, so a psychic entity does not have much control over their sentience. The type of creature that would occupy a cow might be less sentient itself, say the equivalent of plankton or coral to us.
Gameplay
Psychic abilities are available to two character archetypes:
Reason-based
Telepathy and clairvoyance are the main skills offered by a purely intellectual grasp of psychic ability. They can communicate and retrieve concepts, but are less capable of effecting concrete change through their abilities. Reason is nearly as effective in training psychic resistance as Influence.
Lore-wise, Reason-based abilities are the mundane creature manipulating the thoughtforms of the psychic plane.
Influence-based
Much broader range of skills, making use of emotional and vital functions. These would be the more "Psionic" abilities to use D&D parlance.
Lore-wise, Influence-based abilities are the psychic creature influencing the mundane plane.
Samsari Communication with Humanity
Psychic entities have always been present, but when observed were historically interpreted as angels, spirits, gods, etc. Their attempts at communication with us are limited on both sides. Anything they communicated to us would be put through our own lens: a planet might become a mountain, if we didn’t know what a planet is; it only gets weirder when you’re trying to understand the message of a trans-dimensional entity.
But some of the message gets through. The origins of many human myths are the direct telling of particular biotes about their own lives. So the Greek Boreas might have a real-life analogue, with every part of his mythos being vaguely metaphorical for its real circumstances.