How do you beat Sephiroth Kingdom of Hearts 2?

Solution 1: First at the beginning of the game while your still Roxas choose the sword. Then level up to mid 60s and get berserk charge. Equip it and while fighting Sephiroth use trinity and berserk back to back to beat him. Also make sure you have plenty of Hi potions.

Solution 2: Use the Ultima weapon.

Solution 3: Level up to level 99 and kick his azz.