Nina's absolute faith that Ryu is a good dragon, in defiance of many others who are afraid of it.
In the second half of the game, including the dialogues in the camp, Rei does almost nothing but complaining. However, after Ryu kills the mount in the desert to save Nina at the risk of not making out of it, Rei will mention how he didn't expect him to have it in him to do such a thing. Then afterward, he will be reminiscing about their childhood together.
Although he never talks, it's obvious that Ryu has strong feelings about certain things. Particularly, after Rei and Teepo "die", he cries once, then all but refuses to for the rest of the game (there's one time when he does it as a Funny Background Event, though). This almost completely defines his character for the rest of the game: When someone threatens his friends or even just the people that help him, he will stop at nothing to defend them, even if he can't. His devotion to his friends is very awesome.
He also defies the "Brood are destroyers" belief constantly: When he's attacked by someone he trusts, he tries not to fight back. When he's told he has to kill someone, he's extremely reluctant. He's almost a caricature of restraint, despite being an unstoppable force of nature, because he just likes people too much.