The easiest way to beat him is to have the proper abilities, Keyblade, and items equipped. Also, having Sora at a decent level helps. Which is about 45 on Beginner mode, 55 on Normal, and 60 - 65 on Professional.
The proper abilities vary based on your playing style. As a personal preference, I have the following equipped:
Abilities: High Jump LV. 2 (1 minimum), Quick Run LV. 1, Aerial Dodge LV. 2 (1 minimum), Retaliating Slash, Leaf Bracer (And any other abilities that increase the number of available combos & speed of MP Restoration)
Items: High Potion x4, Ether x2
Avoid using magic as it will no effect. Conserve it for healing. Keep Cure, High Potion, and Ether in your shortcut menu. Use Retaliating Slash (hit the "square" button right before he reappears after knocking you into the air.
When he performs his huge sword combos on the ground, avoid them by jumping into the air and pressing the Jump button again at the height of your jump. Avoid his flame tornadoes by running the opposite direction and using Quick Run when they begin to draw you in.
Even when employing these tactics, Sephiroth is still an extremely dangerous foe and will take some time to defeat. Good luck!
UPDATE (Computergeek101234): Contrary to what people say, you can beat him at level 45 as I have done it. When he jumps into the air to perform his attack that leaves you with 1 HP, he will stop if you hit him before he says "the heartless angel".
He dissapears with Cloud
on Kingdom Hearts 1 i have no clue but on Kingdom Hearts 2 after you beat sephiroth go talk to cloud and he will give you a keyblade called Fenrir
Get Kingdom Hearts 2. That's what I did. Or you can try and beat sephiroth and all those extra things.
2 ways cheat via gameshark or just practice
around 29 in kingdom hearts 2
Yes, Sephiroth, originally from Final Fantasy VII, appears in both Kingdom Hearts and Kingdom Hearts 2.
Once you beat him, he goes away.
i did mine at level 56....i don't fight heartless or nobodies much..but anyways..56 is the best lvl...at the point on how you beat sephiroth
After you beat him, he tells you to find cloud. when u do so and return to where sephiroth is, cloud and sephiroth battle and they disappear. You cannot find him after that.