Within every entity on Animus dwells three souls each. The Three Souls are known as The World, The Guide and The Self. Spirits whose Three Souls shatter become a vengeful spirit known as a Soul Eater. It is common Ignited One culture to paint marks upon the face, chest and lower body to represent The Three Souls and to protect them shattering. The journey to the afterlife is when spirits are most likely to be shattered, as getting lost or attacked by Soul Eaters is common.

Spirit Walkers are spirits who return to Animus. Spirit Walkers can be helpful spirits, being guardians or guides for those they visit in their benevolence. Not all Spirit Walkers have good intentions however, as some return for vengeance and destruction of the living, these being Soul Eaters. 

For what seems like infinite lifetimes upon Animus, the Soulless Sickness is an ancient ailment that occurred due to the extreme cases of cannibalism after The Spark struck down. The ill became known as The Soulless Ones, or The Soulless, in reference to how those inflicted would lose all semblance of The Three Souls. It is spread through being bitten by infected wolves or beasts, as well as by consuming the flesh of Soulless Sickness tainted meat. 

Surges of Soulless Sickness have been known to wipe out entire clans and groups of beasts in days. Soulless Sickness can remain dormant for years before suddenly triggering, it is very difficult to tell if someone has been infected. There is no cure, Soulless Sickness is a torturous death sentence. Once symptoms express themselves, death will eventually follow.