Like the Harbinger, the Witch is a mystical being who exists outside of time. She is the caretaker of the Tree of Life.
She acts as the guide and note-taker for the Harbinger on its mission to save Urralia.
It is the Witch's responsibility to perform a ritual with the Tree of Life once a Godless-Priestess passes away to send her immortal soul back to Urralia, to ensure Voden does not return. However, when the current Godless-Priestess, Vera, was murdered, her soul did not return to the Tree of Life. Thus the cycle was broken and Voden took the opportunity to devour the world.