How do you defeat seymore

The way to defeat seymore is fisrt you are going to need Rikku, Auron, and Tidus, Mostly Tidus. First when you start the battle, you nned this kind of poisnous grenade, do this twice. Then you have Tidus do luck, then cheer about three times, this will work because when you perform that kind of magic then it will hurt seymore. Then what you need to do is do Blitze Ace. Then do luck again followed by cheer three times. Again do Blitze Ace. Then do luck again, the do cheer three times, then finally this is the last step to defeating him, do blitze ace.