Soul

The basis of all life.

At the core of every living being is their soul. A soul is the pure life energy of an organism, and gives its body life. Souls also store nearly limitless amounts of energy, able to be released as magic spells. Without a vessel or some means of containment, a soul separated from its body will vanish or turn into a Sprite, and without a soul a body turns into a Husk. When properly removed from a body, a soul appears as a small ball of intense flames, usually the person's favorite color. A soul is required to perform magic spells; automatons and constructs are incapable of magic.

If a soul (or the vessel thereof) is exposed to Crucimen-- internally or externally-- for an extended period of time, it can inflict severe mental illnesses on the victim.

Fun fact: Souls are also where personalities, memories, ideas, and mannerisms originate from. If you swap two people's souls, they will still remain as the same individuals in different bodies. This is also independent of sex; a "male" soul can occupy a female body if they so desired.