Rick's main source of guilt is that he feels he's lied to everyone here. As I've kind of hinted in his more recent discussion with Zett, while Rick's been willing to fight, that previous fervor he had to save his world, his friends and his wife, is really starting to fray due to sheer desperation. He's died and been knocked down so many times, and with that countdown staring him in the face, Rick is beginning to wonder what happens if they don't succeed--and if so, how violently he's going to be rejected for promising everyone that they will. He feels that there is nothing left for him except to keep fighting; there's not even enough hope there to drive him, just the sheer necessity to survive. And if that guilt overpowers the hope he has left, then obviously this means everyone hates him, and he is a horrible monster that deserves nothing except to throw his life away to protect whatever is most important to him at the moment. Under the influence of the despair crystal, this would be Nyx.

Battle-wise...well I think we all know that Rick isn't going to be talking much during this, save the beginning, or as he's dying, and apart from the level of depression he shows his mannerisms won't be much different. Otherwise he will probably be a dinosaur. With Yukiko, he will be an invincible dinosaur.

Gomen heroes :3