From the short story, what I can gather is that souls eventually drift into the Lifrestream then plunge into the Underworld.
The sights that were reflected in his eyes, however, were a far cry from any seen by most men.
What he beheld was the aether that comprised all things, radiating life. From the depths of the land to the heights of the firmament, its light shone bright. Here and there, lives that had served their purpose drifted upon the current before suddenly plunging down unto the Underworld.
That he could behold these wonders was not a wonder in itself. Many were blessed with the sight. Yet very few indeed were as strong in the gift as him. As a man focuses his gaze upon the object of his interest, he needed but to direct his attention towards the aether to behold all the lives borne upon the currents. So acute was his vision, he could make out not only the soul─the heart of life─but also discern subtle differences in the hue of each, telling individual lives apart. And by virtue of this transcendent skill, he had often been likened to a denizen of the Underworld.
I think the most interesting part of the story are 2 things.
"Served its purpose" meaning it sounds like it had an end
Doesn't sound like you can just recognize a soul after it reincarnates if that was the case? Or it doesn't reincarnate as a whole? It's likely broken down to have broken down till it becomes a new soul?
Then you have the Ancients - at this point of time seem to be at the peak of their civilization. There isn't war and strife (likely anymore - I mean who knows in THEIR past) and their existence is biologically immortal. They can still have kids. In addition they can manipulate Aether to use in Creation Magic.
From that, and just looking at general studies on population with births and deaths - this Aether rich planet is probably becoming unbalanced in terms of souls returning to the Underworld.
The souls were used to having everlasting life. It wouldn't be surprising the drift of the soul that became the phoenix gave way to other souls wanting to continue their existence as beings...and maybe did something that created a sound...that caused things to go awry?
"There was an accident," Hythlodaeus began. "During the concept's examination,
a drifting soul merged with it─a soul burdened with regret, judging by the being's behavior. It rages against the pull of the Underworld."
As he listened, Hades kept his gaze fixed on the creature, which flew about in a frenzy. No sooner would it dash itself against the wall in an explosion of broken feathers than it would heal itself and repeat the grisly feat. This self-destructive dance unfolded again and again, with the creature occasionally giving vent to its overflowing magical reserves─or fury, as it seemed to him─as fiery breath.
Witnessing the excruciating display, his thoughts poured forth unbidden from his lips.
"Consumed by the fear of death, it thrashes blindly about. It will know only pain and suffering and inflict the same upon others. A pitiful existence."
That's a theory - as we still do not know for sure what caused the sound - but definitely during that time the phoenix was a sign of things going "off script" and giving ideas to fix it with the use of Primals ironically (from what it looks like in how Zodiark and Hydaelyn were created with hearts).
It was previously mentioned/theorized the Lifestream breaks up the soul after death.
http://forum.square-enix.com/ffxiv/t...=1#post5048735
Yet, Zodiark who rewrote the laws is a PRIMAL. Yet people sacrificed themselves so Zodiark can create NEW life.
New life = new souls? I don't think that's what happened. If the planet was effectively dead - it sounds like the cycle didn't start anymore - lifestream breaks things down so that new life can be populated. No new bodies to house the souls. Zodiark may have created a "River" so that the "lifestream" can flow again. Those that sacrificed prior to Zodiark was broken down to the old system laws. Zodiark had to reconnect the pathways so the lifestream flows again.
I think somewhere in there it was realized you can't have the same longevity going on - so you create beings with a finite lifespan since it seems new souls can't be formed from the bits and created again - so the souls are now in a reincarnation state?
This looks like where the dissent happened vessels and state of being - in terms of souls. Do you keep the system where lesser vessels are created for shorter lifespans so they can return to the lifestream in the new cycle, or do you bring back the old Ancients with long lifespans even though it may be disrupting the balance of vessels able to house souls?