Anima

Anima is the metaphysical matter of spiritual bodies, anima exists in a sort of chicken or egg relationship with Aether. Anima is the result of memory and sensation being catalyzed by Aether during the process of dreaming. But Aether is produced by Anima and no other generation source has yet been found. So which came first? The Aether? Or the Anima? Dreams and memory are the obvious answer, but monkeys and other sentient animals have memory and dreams without, save for a few reincarnates and possessing ghosts, producing Anima or having souls. 
Unfortunately, forming a soul is not as simple as having a sufficient quantity of Anima; it has to be forged around an Ego. Any Anima which remains unforged is prone to sublimating into the environment, like dead skin cells. When Anima leaves a physical body, it takes with it the memories, and the ability to recall them. This happens more than most people think, but is also less dangerous than believed by those who learn of this fact, as lost Anima may be recovered by returning to the site of discarded spiritual matter and "triggering" the stored memories. 
Anima becomes a permanent part of the spiritual body when forged, and numerous religious orders have grown up around the methods of forging. Unfortunately for the spiritual growth of the masses, many soulsmiths guarded their knowledge jealously, even in religions built around the sharing of such knowledge, limiting it first to priests, and then later to gods as they developed. This has limited the definition of new souls, which has been seen alternately as the solution to a problem and an existential problem in or itself at various points throughout history.
Anima comes in several qualities, depending on the density and organization of the material. 
* Anima(simple) which is the density of plasma flame. This is the density at which anima forms and can only be seen by trained professionals.
* Ectoplasm, which is the gaseous equivalent state. This is the anima most commonly observed, due to it being the density of most first generation souls upon their mortal end. 
* Ichor, which is when the soul runs like water. Syrupy in consistency, Ichor is the densest form one might see in a wild ghost, as at this point most ghosts would know how to join an afterlife club or reincarnate. 
* Mordite, which is when spiritual matter solidifies. A soft waxy substance when not under the control of an ego, this is the density at which psychics and magic users operate. 
* Vorpal, the singing metal, is what happens when Anima Crystalizes. Vorpal anima only forms around legends, gods and soulsmiths.