So, I know that after the Sundering, the souls in the Underworld/Lifestram are now basically washed clean of their lives memories and then set up for another cycle birth and death, however, when it comes to presundering there was no mention of a soul being reborn. We were only told that a soul could manifest through natural means by the will of the Star. Now where I'm slightly going with this also was that if there was no rebirth or reincarnation could that have been a reason why the Final Days happened. It was a sound from the planet and the in Through his eyes it did pretty much say that in a sense the underworld was downwards, well the description used by the story was Emet could see the souls traveling upward to join the Aether then head straight down to join the underworld.
Also, seeing as how right after that they had to send a soul there due to it raging against its own death and, for lack of a better term, possessing, even if involuntary, the pheonix concept that was created.
It could have been that other souls felt the same way and that ended up causing such a discord that it threw off the entire balance of the Star and created the end of the world. It could also be why, Venat and the others decided to create and summon Hydaelyn due to the fact that while Zodiark saved the world from being destroyed, said balance would have ended uo teetering on the brink again.
Any thoughts on this?
Edit: also instead of the souls rising up it could havr just been the over abundance of souls causing the balance to become a skewed.
Edit 2: if this has been touched upon already I'm sorry, I went through 10 pages of forum history to look but then gave up.