This other one-shot, here...
Title: Not Being a Hero
Tidus never really wanted to be a hero. Most of his life was spent in grim determination to be better. Better than Jecht. Better than everyone. Better than Tidus. Best. He acknowledges, wry and slightly bashful, it might be selfish. We know all about that, don't we, a snide voice in his head whispers, when Yuna speaks about being happy for others. We know about selflessness. We know how not to do it. He casts around in his head for whose voice it is. He scowls and shakes his head fiercely because it's his own.
He doesn't like it in Spira. He's not best there, he's just there. He's not even the best guardian, because Lulu can cast the spells he can't and Auron has got the stamina he hasn't and Rikku has the technological skill he doesn't and so on. And for the first time in only a few years Tidus is second, third, fourth, anything but first. It might have been better to never know that taste of triumph, whispers the snide voice, but Tidus has never given up on anything he wanted before and if someone questions the blisters on his hands from constant sword practice, he only has to grin. "I have to keep Yuna safe, don't I?" And he'll do it best.
It's always strange to return somewhere, Tidus thinks, because in the end it's all selfish anyway. He tried --God, Yevon, Sin, whatever was out there knew he'd tried-- but it all came down to that he was willing to let them live without him, but he wasn't willing to live without her. Because when you find something that makes you best, best at everything, best at nothing, best at being, it's hard to let go and anyway Tidus has never been good at giving up what he wants.
And eventually he realized he didn't want anything anymore and perhaps it was all for the best anyway.