Whenever a human dies on Aransula with an unfulfilled purpose, it has a small chance to remain on earth as a wandering spirit to torment mortals on the physical plane out of frustration and resentment.
That’s where the Castel comes in, sending spirit trackers to banish vengeful wraiths from existence.
The hypnotic pattern they display in their mantle is supposed to remind spirits where they belong before shoving the ritual dagger into their ectoplasm to dispel them.