:Spoilers: Do not read if you hate spoilers!!!
How to defeat the boss...
First put on protect, so you don't have to heal so much.And use normal attacks, unless he is beginning to use his ultimate attack, you should see a green shine and this normally allows you two shots before he attacks. During those two turns, use the G Beam, it does the most damage. Then use normal attacks. The protect should insure you won't receive more than 1000 damage from his normal attacks and a little more or less than 1500 from his main attack. Make sure to only heal if your HP should go less than 1000 and not during those two turns he is powering up for his big attack. Switch to Tripple Shot once you are unable to use the G. Beam and then move to using Purple Vortex once you have run low on EP. This will help you conserve MP for healing. Once the boss has reach close to 1,000 HP, it's time to be a little bit more worried if your opponents attacks, because your protect will suddenly disappear. So make sure your HP isn't below 1600 when your opponent is close to 1,000 or you may instantly lose. It shouldn't take much more and you'll win with this strategy.