Essence within every sentient creature. Once the body dies, the soul passes into the Spirit World by way of the Ferryman.
Many spells, items, rituals, and personal actions have the capability of adding Corruption to one's soul. This taint makes one more susceptible to ill effects.
Many spells, items, and rituals have the capability of removing Corruption and its lasting negative effects. These methods are typically associated with Light Magic and Jade materials.
Those with a resilient Pure Soul are inherently good people - pure of heart, with unshakable faith in what they know to be the right course of action. Despite all odds, they seem to never lose hope, and never give up on their friends, even in the darkest hour when all seems lost. As such, they can become easily identified targets for corrupted creatures or items.
Certain spells of the true Infernalist magic have the ability to damage a soul. The spell is called, "Shatter Spirit."
"There are no known successful ways to repair a damaged soul, other than returning it to rest in the River."-The White Lady of Bones, 1715