first set your short cuts with curaga, reflega, elixer, and whatever else you want. then i would definitly have:
second chance
once more
beserk charge
aerial dodge
counterguard
guard
upper slash
leaf bracer
and any other combo abilities you want to use. ABSOLUTELY use ultima weapon too. you need the strength and mp hastega. make sure you get that first reaction command, then jump in straight away to attack. when you are getting near the end of your combo use square to smash him into the air and then just keep beating the crap out of him.
if he transports away just wait for him to reappear and use guard or just hit x at the right time to block him. if you do block him immediately attack with an in-air combo.
when he summons the dark energy balls, make sure to cast reflect on yourself or use guard to hit them towards him. when the pillar of flame appears around him, just run away (duh), and wait for it to stop. when you hear him say "sin harvest angel" immediately lock on and and glide towards him and hit him until he falls to the ground. or you can just lock on and use trinity limit. but, whatever you do make it fast.
if he is successful in casting that spell, use an elixer right away, and watch out for the reaction command "block" to reappear. when he summons the fireballs, glide around and watch for opportunities to strike and get in a good combo. but be patient and watch your health.
if you are low on magic and your health is low just glide away from him and stay away until your magic builds up again. above all else keep yourself healthy and get in combos when you can.
this fight took me awhile, so dont worry if its giving you trouble.
hope i helped.