How do I increase my hp in chapter 5?

[strawberry]

I'm in Chapter 5 on Xbox 360 so I'm playing as Hope. Hope has 550 HP and Lightning has 680 HP. Every time I go against the big Feral Behemoth (the purple one, not the others) it uses Heaves and I die instantly. I watch tutorials and the all have 600+ HP. I go to the Crystarium and I maxed out everything for him and I cant move on. Can someone help me?

[.simon]

You could upgrade some accessories. There's not much you can't due if you've run out of CP. Try to avoid them if you can't beat them. Are you forced to fight one?