Lately I was hungry for huge, epic battles so I went back to every games in which you can fight Sephiroth and had a rather nerve-wracking enjoyable time.
By the way, why is Sephy so much harder on Kingdom Hearts I? Its insane. It takes like an hour for his health gauge to start to move!! and after that he has like ten or so bars to go through, not to mention he can teleport behind you, and instantly kill you. I have no idea how I beat him last time, I had to have cheated, I mean come on!
On KH II, all I had to do was get the Ultima weapon, set all my item slots to hi-potion, and equip MP Charge. Having a string of near-unlimited combos really cuts his health fast. I try to hit him when he's casting Heartless Angel to cancel it, but other wise have Curaga prepared. Meteor is a powerful move that can kill quick, but its not so hard to dodge. The most annoying thing about him to the spheres of darkness that surround and attack you.
Oh yeah, and why does KH I and II have Sephiroth's eyes blue!? They're %#@*ing green! Boy, that felt good to get off my chest.