kingdom hearts 2
Kingdom Hearts is a type of RPG, that Disney and Square-Enix did as a collaboration. There the original character Sora ventures out of his home world and meets numerous characters from Final Fantasies and Disney games while searching for his buddies. It seems he has to find King Mickey and save the world while at it, too. Sound cheesy? I know it does, but the game is so much more!
You meet Rikku in Hollow Bastion, where she, Yuna and Paine are working for Maleficent. See, the YRP are...something -Jiminy never really did find out what-, that have a weakness for treasure (Rikku is often portrayed as a thief for a reason, I suppose). Maleficent bribed them into working for her to destroy Sora by promising them big treasure. In the end they do end up working with Sora instead of against him, though (even give him a keyblade!).
Rikku can be seen in a variation of her costume in FFX-2, and she is pretty much her hyper self. Actually so much, that she almost gave out YRP's intentions the first time they met Sora.
Good Kingdom Hearts -sites:
KH2.co.uk (<-- must visit!)