Ryoma starts out as cold, aloof and very much stuck in his own little world where he is the best tennis player ever. One thing one has to understand about Ryoma is that most of his life revolves around tennis. The parts that don't revolve around tennis revolve around eating, sleeping… or his cat. He starts out as extremely socially awkward, making enemies right and left with his holier than you attitude, but he also gains quite a bit of fan following among his classmates. His cool ways impress them - especially the girls.
Ryoma in the beginning really isn't one for team work; he has been growing up in the States where he played tennis alone, and he actually scored gold in the US Junior Open several years in row. Moving to Japan seemed like a waste of time to him, but, being only twelve years old, he really didn't have much of a say in the matter.
Slowly, over the course of four very intense months that he spends in the school Seishun Gakuen's tennis club, he slowly starts to change. Melt, if you will. He discovers that he likes his teammates, and his first real friend – Ryoma has been quite the loner before – is one of said teammates; Takeshi Momoshiro, Momo for short. He plays doubles for the first time with Momo – and it is a disaster, but let's not go about that…
When Momo is in a slump, Ryoma shows for the very first time that he really worries about someone. When the team learns that Ryoma will move back to the States, Momo is extremely upset, even crying. Ryoma, in turn, seems visibly upset as well. But not only Momo, but the rest of the team as well, means a whole deal for Ryoma. Before going back to the States, he plays a game against their team captain Kunimitsu Tezuka. In that game he uses each player's signature move, crying openly while thanking everyone for what they have done for him.
He moves back to America, but not for long. His team is entering the Nationals, and he wants to be with them to back them up. He flies back to Japan to join up with them and the team struggles through the Nationals together, strengthening their bonds even more. Ryoma hasn't lost his cocky attitude, but he has softened considerably, something that becomes quite obvious after his grueling game against the best tennis player in the junior circuit in Japan; Seiichi Yukimura.
During the game Ryoma is forced to go completely beyond his limits, finding the core of what makes him devote so much time towards tennis; he finds that tennis really is fun and exciting. He can really let loose and just enjoy the moment as he plays. He seals Seigaku's victory, earning them the title as Japan's Nr 1, and as they cheers for him, he breaks out in a bubbly, innocent, and carefree laugh. For the Ryoma at the beginning of the series, this would have been unthinkable.