When thinking of the main characters(the eight), i think there would be only one of them who hasn't got a mayor roll, i mean, if he didn't exist, the story would have continued. Guess who?
No not Quina: S/HE found the way to the Outer Continent! Without Quina, Zidane and the gang would have taken a MUCH LONGER TIME looking for that tunnel!
No: It's Amarant! Altough it's my favorite character (warrior monk
), back in Madain Sari, when Lani held hostage, i think Zidane could have taken care of the bountyhunter, without the appearance of Amarant.