Aeons are weaponized ghosts, in short. Auron, after dying, became a ghost, not an Aeon (that’d require someone capable of tinkering with ghosts and someone to summon the manipulated ghost) and found his way to the illusion (Dream) Zanarkand to honor a request from Tidus’ father. And the Dream Zanarkand is part of the summoning that keeps both Tidus and Sin alive.
About Auron and Aeons (spoilers)
Aeons are weaponized ghosts, in short. Auron, after dying, became a ghost, not an Aeon (that’d require someone capable of tinkering with ghosts and someone to summon the manipulated ghost) and found his way to the illusion (Dream) Zanarkand to honor a request from Tidus’ father. And the Dream Zanarkand is part of the summoning that keeps both Tidus and Sin alive.
Okay i need to replay that game, i have no idea what you’re talking about hahaha