The text below represents an accurate (though not complete) high-level view of the Cosmology of the Campaign. Most characters will not know all of this information, and will view what they do know through the cracked lens of their own background, culture, and Traditions.
However, this is what the GM considers to be the minimum level of information required to make informed choices about character creation.
(For a PC to have this level of knowledge, they would need to take Illuminated, or Unusual Background: Spiritual Mechanics Training 5 put at least 1 point in Hidden Lore: Spiritual Mechanics.)
Once a Player makes a choice as to the general direction they are taking their character, the GM can elaborate on the particular aspects and point of view which effect their view and interaction with the Cosmology.
The Spirit World
The spirit world is real. It is separated from this world by a membrane called The Shroud. The Shroud can be penetrated either by a human of sufficent skill, or by a spirit of sufficient power. The “thickness” of the Shroud (and thus the amount of skill or power required to penetrate it) varies from place to place. In haunted houses, holy sites, cemetaries, etc, the Shroud is “thin”, and therefor Mages and Spirits can easily penetrate it. (In GURPS, this means these areas count as High Mana). In places like office buildings or shopping malls, in fact, most of the modern world, the shroud is “thick,” and thus magic and spiritual intervention is rare (Low Mana, in GURPS terms).
Spirits all start as the “souls” of conscious living entities. Once the entity dies, its “soul” crosses over the Shroud into the Spirit World. Most spirits do not have the integrity and coherency to survive the transition. They get scattered into the raw “soul stuff” of the Spirit World, losing their consciousness. Extremely “strong” spirits have enough coherency to retain their consciousness in the spirit world. (In GURPS, this typically translates to high Will attribute).
Once a spirit has crossed over the Shroud, it needs constant sustenance to survive in the Spirit world. This sustenance is provided by the application of conscious Will by the living. In most cases, this Will is provided through simply remembering the dead. Acts such as visiting a grave, rereading a letter, or looking at a picture provide enough Will for a spirit to eke by, holding together in the afterworld. However, once everyone that remembers that spirit dies, the soul eventually “starves,” and passes into nothing.
However, the more thought, energy, and action applied to on behalf the Spirit (or the memory of the entity that became the Spirit), the more sustenance the spirit gets. In this way, some spirits can maintain for hundreds or thousands of years.
A rare few Spirits are worshiped. And these entities gain more and more power as the intensity and frequency of worship increases, and the number of their worshipers grows.
If a spirit has enough power, it can learn to push against the Shroud, and effect the world of the living (GURPS: making a Skill roll and expending Will points). Over time and with sufficient sustenance, Spirits can learn to move objects in the physical world, become visible in the World, and even effect the minds of the living. In this way, hauntings, miracles, and magic can occur. The effects can be as small as knocking a coffee cup off a table, as subtle getting someone a promotion, or as complicated and epic as starting a war.
Spritis form the basis of the myths, religions, and magic of almost every culture. Gods and devils, angels and demons, djinns and devis, kami and animal totems are all Spirits. The personality, culture, religion, and language of the original Soul determine the initial nature of the Spirit as it crosses over. But each of these Spirits is sustained by the world of the living, and so the nature of the memories, worship, and Will applied towards that spirit shapes it over time.
Some Spirits have also found ways to inhabit corporeal bodies. Though occasionally these entities are benevolent, most of these “In-Betweeners” are parasites, using the bodies of living beings as direct sources of spiritual energy. This is the origin of demon possessions, vampires, and other darker things.
Quotidian Magic and Weird Abilities
Almost anyone can do “magic.” Typically, this is a small act of propitiation that positively predisposes a spirit to act on the worshiper’s behalf. Sometimes the Spirit acts out of a sense of love or duty that the spirit holds over from their life (spirits mostly retain their human personality, though this can be changed over time).
Often, however, this kind of magic stems from a simple risk/reward calculation on the part of the Spirit. In these cases, the Spirit intercedes as a kind of transaction: the spirit spends a little bit of Will to help the person, with the hope that the person remembers, and repays with even more Will in the future.
Some people, however, are gifted in dealing with the Spirit World. These people either have a special rapport with Spiritual Entities, giving them the ability to routinely receive spiritual intervention, often without even consciously trying. These people have such a strong resonance with the Spirit world, that their mere will binds spirits (or sometimes a single spirit, such as a Guardian Angel) to act on their behalf. This unconscious “magic” can manifest in relatively mundane ways, such Luck (up to GURPS Super Luck), with Spirits constantly interceding on a person’s behalf. However, for some people this can result in weird abilities, such as the ability to spontaneously learn skills (GURPS: Wild Talent).
Mediums and Channelers
Other individuals are extremely open to spiritual possession, yet unlikely to be harmed by it. These people can open themselves up to possession, and let a spirit communicate through them (GURPS Advantage: Channeling). Others can simply speak to spirits in their presence (GURPS Advantage: Medium).
In either case, such individuals often develop some kind of reputation with Spirits (GURPS: Reputation, Spirits Only [Large Class, x1/2]). Stronger bonds can also develop, allowing for such things as Spiritual Allies, Contacts, Enemies, and even Dependents (GURPS advantages)
Occasionally, a human can develop such a strong bond with a spirit that the entity chooses them to become their Spirit Warrior. A Spirit Warrior slips into a trance to commune with his or her Patron Spirit, and awakens imbued with the powers of their Patron. In this way, some humans can display amazing feats of strength, speed, and toughness.
Becoming a Spirit Warrior is something like being possessed, but the Spirit Warrior’s personality becomes an amalgam of the host and the possessing entity. Typically, this manifests as the person temporarily displaying signs of attributes they do not normally have, such as an accent, proclivity, or mental disadvantage they did not have before. For example, Spirit Warriors of Voudon traditions often act drunk, are quick to anger, and swear profusely in Creole, regardless of whether they previously spoke the language.
The most powerful and subtle of all humans who truck with spirits are Ritual Mages. These Souls have not just a natural affinity with the spiritual world (GURPS Advantage: Ritual Magery), but have trained their Wills to bend Spirits to their command (GURPS Skill: Ritual Magic and Variations – see below).
Ritual Mages belong to numberless Traditions. Each codifies its understanding about how to influence and manipulate the Spirits, and passes down that understanding to new initiates. Native American Shamanism, Voudon, and Hermetic Magic, are just a few broad examples of Traditions (and of course, each of these has numerous internal factions, schisms and clades).
Additionally, the complexity of the modern world has lead to the rise of new ways to interact with the spirit world. Many “technological” skills, such as Civil Engineering, Mathematics, and Computer Science, performed at the correct esoteric level, can form the basis of Ritual Spells.