Just bought it today and spent the last couple of hours beating it, but I still don't have Lightning in my party. I spent a while just getting past the first battle with Caius due to hidden requirements that I can only assume was battle time, and I saw the scenes after the Chaos Bahamut fight, but that's it.

I got that little message of "Chaos was Defeated" or something like that after the second fight, so what am I missing? D: