According to IGN, first and foremost, you will have to have sealed the Space Paranoids keyhole in order to find Sephiroth. He appears just beyond Crystal Fissure in the last section of Hollow Bastion, which is now called Radiant Garden, called the Dark Depths. Hit Triangle to converse with him to engage in combat.
Before even attempting to fight Sephiroth, you'll want to have the following abilities and items:
Ultima Weapon (MUST have)
Air Slide
Air Dodge (optional)
High Jump Level 2
Reflect Guard (optional)
Revenge Slash
Combo Plus(es) and Air Combo Plus
Supply of Elixirs (preferably), or Hi Potions -Level 70+ (preferably) with strength & defense 40+ each
The unlikely but successful collaboration between Square Enix and Disney Interactive returns in Kingdom Hearts II; where a darkly-cloaked Mickey Mouse joins Donald, Goofy, and Sora as they continue their adventure into several popular Disney-inspired worlds.
Battling against the Heartless once more, the dedicated group of friends now find themselves up against an all-new enemy threat -- a mummy-wrapped ruler of unknown origin. Also fresh to the series is a brand new meter known as the "Transformation Drive" that allows players to merge with other team members to create more powerful versions of themselves.
New costume designs, improved camera controls, and the answer to lingering plot questions from the first game are also included. Developed exclusively for the PlayStation 2.
Tip! Check out these 65 cheats & codes for Kingdom Hearts II from ign.com.