Ultimate power, a bit of madness, the risk of dying horribly... what's not to love about this.
I like the flavor that bleeds through. These aren't normal sorcerers who gather power through bound spirits. There is an entire ecosystem of ethereal creatures. It speaks to a larger, well-developed world, with enough similarities to standard fantasy to make it easy to grasp and enough uniqueness to set it apart.
This is good. While the concept may not be new, the backstory really brought it to life for me.
I would probably put these in an area where the previous owners (having lived) discarded them. Then, I would herd the players to this spot, without weapons of their own (perhaps they were captured and are attempting to escape.) Ok, this sub brings out the evil GM in me, but I like to keep my players on their toes.
These would also be a good tool for conmen. Sell them to unsuspecting adventurers, impressing them with the cutting ability, then set upon them on the road, knowing that they would be hampered. Steal from the corpses, and repeat.
A tantalizing glimpse, but I would also like more detail. Perhaps an intro where the soul dies for the first time to answer the question of how he landed there. Maybe even a plot hook on how to get the adventurers in and out of such a hell, either looking to save a lost comrade or on a mission for information from the deceased (who would quite likely demand release as payment.)
I'm witholding my vote for now.
Excellent writeup, Drackler. Not every being must be of world-shattering proportions in order to be useful or make a game enjoyable. Sometimes a little subtlety can kick off larger events or have just enough impact to affect an important outcome.