I think Tidus and Yuna are better together than Tidus and Rikku. I'm not really sure who would be a good mate for Rikku since her personality is quite different in FFX and FFX-2. Maybe Rikku and Buddy? Oh, and for the record, "tikku" is Finnish and means "a stick", as in :twak: , so I think that explains what would happen if Tidus and Rikku got together.