Rikku is in essence a sidekick character. She's got a lot of experience fighting at this point. She's fast, accurate, and evasive: not the party's tank, but closer to the rogue/thief archetype.

Her leg-pouch has healing potions in it, as well as protective items that can assist others; i.e., this item can form a shield that means you only take half-damage from certain attacks.

Rikku's native language is called Al Bhed. Lulu and Reno both speak it, as well.