Voidkin

Sometimes a member of the Dark Pantheon of Others will select a mortal to represent them within Tolcairn. These hapless mortals then become the Chosen Ones of the Void, colloquially known as the Voidkin. It is speculated by Void scholars and the Abbey of the Everyman that each Other in the Pantheon has their own reasoning and process by which they choose a Voidkin, but little else is truly known for certain. Some Voidkin mutate horribly, becoming monstrous, twisted abominations, some maintain their ordinary, mortal form. Some are chosen at birth, some are chosen on their deathbed. Some actively seek out the Pantheon to achieve this status, some are picked seemingly at random.
The one thing in common with all Voidkin, regardless of their Other, is the Pantheon's Mark, an eldritch symbol that appears somewhere on the Voidkin's body akin to a tattoo. All attempts to replicate this Mark in any way, shape, or form, ultimately fail. Likewise, removing the Mark proves to be impossible - even removing the appendage that the Mark is on only causes it to migrate elsewhere on the Voidkin's body. Through the Mark, the Voidkin channels the power of their Other and the Void; while it takes time to truly master these abilities, even an untrained Voidkin is extremely dangerous, as they shine in the Void like a beacon that draws the Others to them. Moreover, should a Voidkin become experienced enough, their physical and magical potential could easily outstrip the strongest soldier and the wisest mage. It's suspected that it was a Voidkin who caused the Great Burning at the beginning of recorded history, and so the Abbey of the Everyman's policy regarding them is to put them to death immediately upon discovery.