Aether

[Keroa]

This also neatly explains why the Primals require not only aether and crystals to exist, but also worship, as well as how beings like Good King Moggle Mog the XIIth, even an ACN's Carbuncle can exist despite not being a Primal - with enough aether/crystals and a strong enough will a person could make even the most abstract or intangible desire corporeal. Pretty much, a 'wish made manifest'.

Oh goodness, this is actually an aspect of Crystals I have not even thought to question, as well as a door to more questions, I am still curious as to how crystals are formed. I know how they form in our world, but I wonder if the process would be similar?
Also: how would you think, if a persons Aether has become corrupted, to purify that coruption? Assuming any new Aether introduced would also become corrupted and ultimately take it's toll on the body (like what you see in Pharos sirius)