Okay when Tidus says it's my story, essentially it's everyones story. Anyone could've been up there on the ledge in Zanarkand reminiscing and sharing their individuals stories with the audience. But Tidus' would probably be the most interesting, with the whole Zanarkand thing and Jecht.

We'd have to look at it in terms of who sort of leads the group through Spira. And I'd say Auron, Tidus and Yuna. Auron, because they all look upto him for guidance as I said. Tidus, because he just played a main part. And Yuna, of course because she's a summoner and it's following the story of her and her guardians.

Without Yuna, there wouldn't be much of a story yes. But if we look at it like that we might as well say Sin was the leader as he pretty much is a common element in everyones story and.. yeah, is pretty much the plot.