I've always found Riku's design in KH2 very interesting. In KH1, he's so much muscle it's hard to believe he's only 15. In KH2, he's grown taller, but he doesn't have the same muscle mass he did before. He's thinner (notice the arms), indicating that he's weaker. This correlates perfectly to his confidence. In KH1, he was cocky and prideful, but in KH2 he's broken and afraid of himself. I love that they communicated this vast character shift through his physical appearance.