Vaan and Panelo. If you take them away from the story Ashe and Bashc are still fighting for the same thing, to free Dalmasca. Sure Vaan wants to avenge his brother but almost every other character wants to avenge someone aswell. To me he's just sort of an inroduction to the game, kinda like how Roxas is in Kingdom Hearts 2. And Panelo is just sort of 'there' with no real purpose.