Beatrix Beatrix

[Mirage]

Maybe she's one of these people with just one name, like Rihanna, Adele, or the cast of Final Fantasy X.

Tidus Zanarkand!

[BustaMo]

Tidus Zanarkand!

I think Kimahri is the only one in the main party that has something even remotely close to a last name with "Ronso", but that's more of his species/tribe, than a last name. I'm pretty sure in the game he's referred to as Kimahri Ronso throughout the game.