Or Cait Sith's "Game Over" Limit Break, which instantly kills any boss. If you're insanely lucky that is. Magic Counter-Full Cure tends to buy you enough time to get the slots right, but it'll take many attempts.

W-Summon isn't utterly necessary, it just makes the job a bit quicker is all, and Knights Of The Round will need to be at least level 4 (so you can summon it up to eight times). Here's a strategical spoiler if you don't mind knowing how much HP it has; I personally don't like to look this stuff up before defeating a boss for the first time. (SPOILER)Emerald's got 800,000 HP, Ruby's got a million. I have no idea how much HP Emerald's eyes and Ruby's tentacles have though.

Ruby's a lot easier than Emerald because in the end it's usually fighting more or less alone: The tentacles go down quite easily whenever it decides to summon them as opposed to Emerald's eye things... and Aire Tam Storm = yikes!

*No you morons, "Game Over" IS the one where you automatically win. The one that kills your party is called "Death Joker". I'm not having this conversation again, go look for the damn video on YouTube.