Now save your game and be sure to find items that will increase Lulu’s magic power and have Wakka equip a weapon that can inflict a Darkness status. When you’re on the airship you can take some time to look around, but after you have made adjustments to your weapons and armor, save your game.
Now when you return back to the bridge talk with the captain and you’ll know where Yuna is. Now talk with the other party members and Cid and then try to leave…you’ll eventually know that the Guado have snuck aboard. Now head around to the back of the ship and check the window to find Evrae.
Although the HP is quite intimidating, you will have to deal most of the damage. Cid will do some damage by releasing his 3 sets of salvo, and each salvo hits 10 times…but each missile only does 200-350 HP of damage. At the beginning of the battle Cid will tell you to let him know when to move. Move just before Cid’s turn to attack with the ship’s weapons. the Photon Spray will hit multiple times to every character, doing up to 300-500 HP of damage…so be sure to heal and keep your HP up. Your best bet is to stay far away from the boss and use your remaining salvo. Note that even though you may have the Poison Ward ability, it sometimes fails against this boss. I don’t know why either. I wasted a lot of Gil buying those Softs for those abilities(Poison Ward), ugh. #$@%!! You can fight close and use Dark Break against it with Auron, it’ll at least spare you some damage. When you fight too far away for too long it comes at you with an attack, then running back becomes useless since it will use the attack to come back every time. If Evrae uses Haste, use Tidus’ Delay Buster or Slow to counter it. Don’t use it when Evrae is not in Haste mode though, otherwise he will be when he uses Haste as a counter to Slow status attacks. My Auron typically does about 1100 each hit, not sure about your characters, but whichever character you have that can deal the most damage with physical attacks should always be up front when you are close all the time. Only Lulu’s Overdrive works at a far distance however. Make sure to use all 3 of your Salvos against it, you’ll definately need it in this amazingly long battle. Also if it uses Poison Breath, use an Al Bhed Potion by Rikku, which is amazingly useful in this battle. She probably won’t do you much good other than to use Al Bhed Potions. Blinding and slowing Evrae down is the key to winning this match. Be sure to worry about your HP first before reviving downed allies.