all right. make sure u have guard, guard break, trinity limit, once more, retaliating slash, and second chance set. also put on ur shortcut bar hi potions, elixirs, reflect magic and cure. using oblivion or ultima weapon works really well, too. if u have quick run, get rid of it. ppl say u should belv 70 but i beat him at lv 55 so lvl is only a number. the once more ability makes it so u won't die when he uses his combo so don't worry about that.
now when the battle first starts use triangle to block him. when he is walking to u
run to him. he'll start attacking like mad. use guard continuosly until he stops.
press x for guard break. then u keep attacking him till he disappears. if he uses
an uppercut on u and knocks u in the air, wait until he appears to beat the hell
outta sora and then use retaliating slash and attack him. with perfect timing this is a nice
counter. watch out for the reaction command block to appear again. repeat this
till half his life is gone. when he rises in the air to use sin harvest use trinity limit
which uses all ur mp so it is strongly suggested u use only hi potions and elixirs to
heal urself. after using trinity limit keep attacking him again. when he uses
meteor, glide around the field to dodge. this is the best way to beat him.