I recently managed to get the Rikku scenes. They were excellent. (SPOILER) Eg. If you say that you want her rather than Yuna, she jumps off the path in Guadosalam, saying "Maybe someday!" in Al Bhed. I think that was playing hard to get!

I did it by fighting with just her and Tidus and getting him to heal/remove statuses from her a lot (about 20 to 30 times).