[quote=@Oraculum]
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?[/quote]

It's not a thing that would come up or be mentioned often. It can explain how Loki's demons weaken souls and eat them and why Katharsos does what he does (among other things) while not being intrusive enough to warrant anybody taking note of it 99% of the time. I think you greatly overestimate how much this would affect other mechanics or the story at large.

[quote]
...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.[/quote]

If you weren't on the same page, I think we've come to decide that heroes are by default made immune to soul fraying. It's a mechanic that would only really matter for undead that stick around for a long time, or for mortals that find non-divine ways to extend their lifespan far beyond what is natural for them.

[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.
[/quote]

The most obvious solution is that it'd be cruel to let a soul slowly go crazy and suffer as it degrades into ash over what we can imagine as a very long process. Katharsos is putting the dying horses out of their misery, so to speak. Furthermore, I'd imagined that a soul "fully degrading" would take extremely long lengths of time, so KAtharsos burning them would greatly accelerate this process and prevent the vast majority of souls being in a useless and half-degraded state at any given time.

[quote]
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:

<Snipped quote by Rules on Might spending>

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.
[/quote]

This actually got raised as a point and discussed among us GMs as the other two talked over my sheet in our PM convo. We already have something of a consensus regarding it, I think.

That above point refers to taking a soul of a very recently dead person or creature and putting it back into a body prior to it being sucked up by the Vortex of Souls and eventually burnt. There's a backlog of souls sitting in the Sky of Pyres that could be rescued and the process a soul takes in order to get up to the Sky also takes time, so there's a vaguely defined (but finite) window that gives gods a reasonable chance to take this action.

Resurrecting something that died a really long time ago [b]is[/b] rendered impossible if its soul was burnt, though. This imposes a bit of a ticking timer, which isn't something that I think to be necessarily bad.