Quest For The Ultima Weapon

Right now in Kingdom Hearts Final Mix, I'm just working on getting all the synthesis items, the main one I'm focusing on is the Ultima Weapon, which is the best keyblade in the whole game. Although the ingredients to synthesize them are in Japanese, I have a translation guide, so I know what I need to synthesize them. Once I get this keyblade, I will attempt to face Sephiroth in the Olympus Coliseum. If you don't already know, he is a lot harder in Kingdom Hearts Final Mix than in the original Kingdom Hearts, especially in proud mode. I'm already at level 84 so I should have no problem facing him, but I just want to make sure I can beat him, and it would be a lot easier with the Ultima Weapon. An image of the Ultima weapon is posted below.