"A soul," says Hazel, "is... a bit like the skin of one's mind. It contains and strengthens the mind, and provides a barrier between it and the outside world. Colloquially the soul and the will are often conflated, but the soul is not the will, only its framework or substrate. A demon does have a will, but without a soul to mediate between will and world, they are powerless in all the realms the will normally governs—resisting transformation and injury being foremost among those. I believe, though I cannot confirm, that demons also cannot gain strength or endurance by training the body: being essentially a self-imposed transformation accomplished by the unconscious will, it should be impossible without a soul. I also theorize that demons have a hard time navigating—but I'm getting off track. So far, evidence tentatively suggests that you do have a soul. But the evidence is somewhat indirect; there could be other explanations for each observation. A more direct test is needed. As an alchemist, of course my mind jumps to alchemical solutions first—but alchemical solutions are slow and indirect, and we have a different kind of expert on hand just at the moment."