hehe.. Rape Sauce..
Oh,anyway the key to defeat him is to have your limit ready and to be about lvl45 to lvl99 as i defeated him on 57.make sure you got Curaga and cure limit on the abilities,as when you cast cure it keeps curing you until mp charge runs out.also,try to get the oblivion or ultima and the gaia belt,the belt gives 4 defence.
if you kill seprioth you get Fenrir, it has 7 strength!! (and 1 mage)
He,rape sauce.
You Like Kingdom Hearts?? Well it just blew up!!