I thiiink it's playing when Yuna holds some sort of little speech before facing Shuyin or after facing Shuyin...or something like that too? Or maybe I'm just fuzzy, been a while since I played that game now. I loved that theme anyway, sad in a (bitter)sweet way, kind of like Yuna. (Though in FFX-2 she was mostly just..sad.)

The soundtrack of FFX-2 was it's ace. Mostly fun, but with some really nice sad themes too.