[Spoilers] Death and reincarnation

[Kokomi]

snip

This makes sense - had forgot about the bit where Ascian souls retreat into the rift instead of returning to the lifestream. In that case, is the population of Ancients fixed (one has to die for a new one to be born), or otherwise where do new Ancient souls come from?

Along the same lines, for the "Zodiark created the lifestream" theory to work, new aether needs to be created at some point. Otherwise, how would this plan of sacrificing something he created back to himself result in a net gain, unless the lifestream can somehow generate aether from a source other than Zodiark?