In FFX, Rikku and Yuna's relationship isn't elaborated very much. You know that they're cousins, she affectionately calls her Yunie, and that Rikku is an Al Bhed and so on. As they journey together, Rikku becomes more and more emotional when it comes to losing Yuna. During the very heart-wrenching moment at Home, Rikku breaks down and tells Tidus that Yuna will die when they defeat Sin. And then, when they get to Zanarkand, Rikku's love for Yuna is very evident when she breaks down again. Rikku can't stand the thought of losing her, and she would go through almost as much as Tidus to save her, as they both try hard to think of a way to save her. The bond between Rikku and Yuna is stronger than that of normal cousins, because they were put through so much together. Rikku would do anything for Yuna, and she tries pretty hard to.

In FFX-2, Rikku and Yuna are closer than any two cousins could be. Rikku has been with Yuna for so long and has gone through so much with her that they trust each other with their lives, and rely on each other as well. They're always dancing around together, running about and annoying Paine like there's no tomorrow. That kind of bond is very strong... and annoying, at times. Rikku is a lot more cheerful because she succeeded in saving Yuna. Rikku's only real emotional scene is after the concert in the Thunder Plains, when they speak to Maechen. Rikku talks about what it was like trying to find a way to save her, and what it felt like. It's at that point where you really see her emotional side, and that she really does care for Yuna.