AH, yeah, I had the same problem. It took me more then a couple tries (three :mog: ). I got fed up with being beat so easily, so I sat there right next to the save spot, and trained for a LONG time. Then he was really, really easy. My advice would be to get all your aeons overdrive bars full, esp. Bahamut's, if he can break the damage limit yet. That will definitley take him down for you a little bit. Also, if you have it, cast bio, or use something that poisons him, because he actually isn't immune to it! Maybe you might want to ty hurting the mortibody thing. That's how I killed him. I did some big attack, or something, then the mortibody took about 4,000 health from him, and killed him. Maybe you can use him to your advantage?

Sorry, I did that part quite a while ago, hope that helps. At least you're stuck on Seymour FLUX. I got stuck on Natus for what seemed like forever, although everyone else I know says he was a snap.

Good luck! You're bound to beat him sooner or later.