^Well, the emphasis would've been on friendship. Xion was put in the game so that-in a natural way-there would be a cause for Roxas leaving.
her finding out the truth causes a rift between her and Axel. Axel decides not to tell Roxas for worry of him being upset. The rest of the group treat Xion like sh*t. She herself leaves willingly and gets involved with Riku, DiZ, and Namine. Axel forces her to come back, causing not only the gap between them to grow bigger, but now him and Roxas. It happens again. Roxas continues to see flashes of Sora, and he longs to find out about him. Xion tries to leave again, but is forced back again and reprogramed to destroy Roxas, but on her next mission, she leaves yet again! Roxas learns the whole truth from Axel, making him angry and he leaves all bada$$-like just walking out of the castle slaying Nobodies who get in his way. Xion then tricks him into killing her.......two days later. I mean, what was he doing day 256?
Character-wise, development isn't the biggest problem. Practically every new world/experience teaches Roxas something new. Axel hates babysitting, but that doesnt mean he's pissed at Roxas off the bat. Maybe it was an easier BS job than he thought. Dilan clearly must have loved and lost and been convinced by people who havent loved at all that he was better off, otherwise he wouldnt have been so sure it's a delusion. Saix, in this game, doesnt have character development but his former friendship with Axel is clear each time they're on-screen together. The only other remote substance in a character is Lexeaus. He's such a thinker and not much of a talker and he's definitely not about to star in his own Late-Night comedy talk-show.
Actually, mentioning Xaldin reminded me of something f*ching hilarious, but only related to the game in part.