How do you defeat Sephoroth in Kingdom Hearts 2

Sephiroth is the hardest boss to beat. You can only find him in Hallow Bastion, in the dark depths, when you have completed every world except the world that never was. His combo can kill you if caught in it, and his moves are deadly. To start out, make sure you have hi or mega potions in your items section (don't use ethers, they only heal mp and will waste time)If you have Ultima weapon, use it. If you don't, use decisive pumkin or Oblivian. Make sure you have lvl2 or 3 glide because glide makes this battle so much easier! (hint: Glide can be obtained by leveling up your final form) make sure you have reflect and cure on, also once more and second chance, because this fight is ROUGH!(Do not put on guard, it will have no use what-so-ever)
He will start out with a reaction command, make sure you hit it or you will get hurt bad. He will use the reaction command from time to time. He will start dissapearing around, trying to hit you, use glide to dodge his attacks. He will then walk slowly on the ground with his sword held up, like he is ready to block something. DO NOT hit him when he is like this, because he will hit you and the combo is very deadly. If he catches you in the combo, don't worry, use a potion or cure because you just got saved by once more and second chance!
He will then use an attack that is one his most deadly of all called "Sin Harvest" He will rise into the air, surrounded by a pink light, then he will say something like "Descend, heartless angel." Once he finishes the word "angel" you will have 1 hp left and no MP. Potions will not help because he will automatically attack you after Sin Harvest. The only way to prevent him from doing this, is by simply attacking him. then he will do the stufff like in paragraph one.
Once his health is almost halfway, he will start using dark orbs that surround you. These will follow you if you try to run or use glide. In a few second they will dive into you and hurt you. Use reflect on the orbs to deflect them back to Sephiroth. If he uses the orbs then does the reaction command, don't use reflect because you might dodge the orbs, but get hurt by the combo. Instead, use the reaction command because it will deflect the orbs and Sphiroth's attack.
Once his health is down to about 5 bars, he will start using a flame attack that pulls you in, but can easily be dodged by using glide.
once his health is down to 2 or 3 bars, he will use his most absolute deadly attack: Super Nova. This is more deadly than Sin Harvest because it is not easy to dodge and is a deadly rapid attack. The sky will be surrounded by flames, then he will shoot meteors at you. Make sure you keep using glide and watch where your going, one wrong move could lead to your death.
Repeat all these steps until he is defeated. It will then show a cutscene where he says he cannot be defeated by you. He then tells you to go find cloud and tell him where he is. Cloud can be found in the square where you start off at Hollow Bastion. He will ask that if you have seen Sephiroth and you have the option to say "Nope" or "Well..." choose "Well..." beuase that means yes. It will then show a cutscene where tifa comes in and tries to beat up Sephiroth. She keep failing. Then Cloud comes in for some Kick-Ass fighting! in the end, Tifa gives Cloud here light and Sephiroth and Cloud disappear. Sora will ask where they went and Tifa will say that Cloud has gone to fight his darkness. She will then leave, giving you something. And behold, the mighty Fenrir keyblade with the best strength, comes with a negative combo. Once you have this keyblade you have bragging rights about your fight with Sephiroth! Congratz!