The soul of any living entity is to be considered as complete and separate from the body. The soul as we know it belongs to the subplanar realm which exists outside of normal space.
The soul of any given creature can be illustrated as a loop of thread. The more massive and/or more complicated the entity the larger this thread. As a given entity experiences life this thread tangles, knots, and twists, becoming an evermore intricate tapestry.
When an entity passes and its soul loses its connection to the realm of the living it undergoes a process of unraveling. Under natural circumstance the thread must be undone completely before it can again find purchase in a new being. The undone state of a soul is called the Central Essence by Warden Philosophers.
Souls are not truly immortal. Eventually over time like normal thread they will irreparably fray unless reinforced artificially, though, even that does not keep the great beyond at bay forever.
These threads can break, like a tear in a tapestry, but they cannot always be repaired in life, often the only way for those breaks to be fixed is for them to take extra time recuperating in the subplanar realm between lifetimes. Taking longer to recuperate in death.
The soul can be destroyed like tread by damaging it beyond repair.
Souls are very much living creatures in their own right as they live, die and reproduce.
Souls do not normally reproduce like living beings, the only instance in which they do are when latent souls are not available to inhabit their offspring, or when a Chimera is born. In such cases the soul will engorge itself on other subplanar entities such as mushi and develop an offshoot that while similar to its sire is new and equal to it, like cellular mitosis. In the case of a chimera the souls of both parents send offshoots and they intertwine.
- Note that souls that reproduce are typically coaxed into doing so by circumstance or action, only the most vivacious of souls will multiply of its own volition.
The souls of the living attract the Central Essence (those souls that have completed their rehabilitation) and when the living reproduce the central essence inhabits any offspring. Souls will often shadow people, places or things as they wait for a new offspring to be conceived. They are often overlooked as tricks of the mind, or in the case of especially curious souls of the higher orders are sometimes mistaken as guardian angels, and a multitude of them can encourage additional births.
No specific type of soul is exactly special. The only true difference between the souls of songbirds, bears, humanity or high dragons is the length of the thread and the experiences it develops due to its mortal form. If one were to somehow artificially embiggen a soul of a lower order it would garner an increase in sapience and intelligence.
A body without a soul is essentially a vegetable, capable of only the most basic functions of being fed and aimless wandering. Some beings especially those of artificial origins may act in predefined ways, but for natural beings this is not the case.
The soul of a being that has died can be forcefully reinstalled into a new body or anchor, but the longer time since the being's passing the less the personality reflects the "original". Memories deteriorate first, then knowledge, then personality, then instinct.
Furthermore souls while do come completely undone between lifetimes, they do become 'stained' from the experiences of their lives among the living, coloring their future lives in unknowable ways.
The Great Beyond, the place that calls to the oldest of souls, as Wardens call it, and to where they eventually disappear is still a mystery.