Yea, I was thinking the top contender would be the son. Masters generally refrain from tournaments in general so their students can show off what they learned. Maybe they confront the master after the tournament, which Kaoru might need Kenshin's help with. I think 16 would be a good age for the daughter, maybe a little older for the son. As for Ryuuto, he's got a lot to live up to, wanting to be as successful as his father both in his swordsmanship an running the family business. I'd say he's diligent and in some ways more ruthless than his father. He'll use any dirty trick to win, including taking a hostage to make the toughest competitors throw their matches.