The character named Echizen Ryoga is the elder sibling to Echizen Ryoma, who plays a significant role in the film. Initially, he was portrayed as potentially being an adopted relative of Ryoma.
Later, Ryoga takes Ryoma, after being disqualified, with him to the USA where the little boy gets qualified for the American team.
In the New Prince of Tennis manga, it turned out that Ryoga was Nanjirou’s son from an earlier relationship. He left Ryoma alone when he got to stay over at his aunt from his mother’s side. It seems that ryoga was quite close with his little brother and cared deeply for him, what is shown by the hard time Ryoga had when he was supposed to tell Ryoma about his departing.