On the topic of souls, I have no issues with souls being finite and any crisis plots that might entail, and I agree with it being more practical for divines to have essences distinct from regular souls. However, I have to object to the notion of soul fraying. As I have said in the Discord, I find that it makes things needlessly more complex without contributing anything interesting or useful to the setting that could not be achieved by much simpler means. Consider the following:

[quote=@BBeast]

On soul decay, I propose this: An intact and healthy body inhibits the decay of the resident soul. Stuff like divine essence and the MP invested to make Heroes heroic further reinforces souls against decay to the extent of stopping decay entirely while they are alive. Part of making an immortal species is spending MP on their ability to keep their souls together indefinitely. [i]Ad hoc[/i] solutions, such as those available to mortals, do not prevent this fraying, and self-made immortals will need to work to maintain their immortality (e.g. a lich needs to keep consuming souls so as to replenish the part of their soul which frays).

On the death of powerful beings, typically their death is brought about by something which weakens the being to the extent that the being is too weak to not die. At this stage, stripped of power, the being (e.g. god, hero) is likely (although not certainly) too weak to resist the Sky of Pyres.

On what counts as a body, it is whatever you have spent Might on to make as a body for your species.

[/quote]

In essence, this amounts to emulating a natural process (aging and bodily damage leading to death) which normally occurs on its own. In such a system, a being would be weakened by having a compromised body, which leads to a decaying soul. But a compromised body results in weakness regardless of the state of the soul within; indeed, even in a cosmology where souls were absent altogether, physical harm would bring one closer to death, regardless of any ulterior circumstances. In addition, a soul's health being dependant on the body's condition could lead to some strange quandaries: would someone who has lost a limb have their soul decay at an accelerated rate? Would someone who has suffered from a severe disease, and then recovered, nevertheless die prematurely because the period of illness resulted in pieces of their soul sloughing away faster than normal?

As concerns immortal beings, divinely blessed and not, soul decay once again adds a layer of intricacy that does not appear strictly necessary. The additional effort (MP) spent in reinforcing the souls of such entities could just as easily be explained by the difficulty of creating physical forms for them that better withstand the advance of time, something that would need to be done anyway if the creator does not wish for them to grow decrepit under the immense age they would eventually reach. Those mortals that would attain immortality by their own means would be in a similar predicament. They might be able to extend their lifespan by some means, but they would have to keep themselves from rotting away in order to enjoy it, and no amount of consuming souls would help them with that. The lich in the example would need to, for instance, drain its victims' life force to strengthen its crumbling bones; that is not to say that it shouldn't be able to strip them of their souls for some purpose, but, as mentioned, fuelling its unlife with them alone would be a futile endeavour by the system's very rules.

Furthermore, soul fraying seems to me all the more dubious since there is no definite description of how it occurs. It was said that:

[quote=Cyclone in the chat yesterday]I imagine a fully decayed soul would just be a bunch of crumbles, effectively a lump of soul ash with a few chunks big enough to retain some memories etc.[/quote]

It's not very clear how this would fit into the workings of the soul as determined by the Sky of Pyres. If the decay is manifested in the soul falling apart, how would it be purified at Katharsos' hands? And, if souls crumble back into ash as they reach the end of their course, why would he need to redistribute their material by artificial means? Far from providing a justification for his work, soul decay might in fact place its usefulness into question.

One last note, not necessarily related to fraying but still linked with matters of death and the soul. I notice the OP still has this point, written before Katharsos was conceived:

[quote=Rules on Might spending]
3 Might: [b]Resurrect a mortal or a hero.[/b] Reaching into the depths of death and plucking back a mortal soul is no easy task, even for a god, and will likely involve a quest to whatever Sphere the soul has gone for its afterlife. The cost for healing or building a new body for said mortal is included in this act. This cost does not cover any sundry expenses incurred during a quest to the afterlife and back.[/quote]

Since in the new system death involves one's mind and memories being destroyed and scattered, eventually going to form new living beings, the feasibility of this might need to be revised.