I think I figured out Tidus' last name. In the beggining of the game right after you give your autographs to the fans. That narrative comes up, it doesn't sound like Tidus, but what he says is definetly describing Tidus. 3/4 of the way into the narrative he says "I say to myself Zanar. what in the world were you thinking" or something like that Is that Tidus?