"Oh, boy. I'm no good with this sort of thing," he said, running a hand over his hair awkward. "Uh, long time ago Zanarkand was at war with Bevelle. Zanarkand had summoners. They summon Aeons. Big monsters that fight for the guy who summons 'em. Bevelle had machines, Zanardkand was losin', so the boss of Zanarkand turned everyone inta Fayth and then made Sin. That snapped his mind, Sin went berserk, so his kid came up with a way ta beat Sin. Someone volunteers ta be a fayth for a summoner's 'Final Aeon', and then the summoner uses that ta beat Sin. Then Yu Yevon pops outta the old Sin, takes over the Final Aeon, an' builds a new Sin around it."