I heard this song on YouTube in a music video giving each character their own theme music, and this was the one chosen for Aeris, but it more fits Cleris than anything else.
http://www.azlyrics.com/lyrics/seal/kissfromarose.htmlThere's also a few music vids on YouTube using solely this song.
http://www.youtube.com/watch?v=x0Pvd86t8D0What do you think, it fits them?
It definitely works, not in the least because Cloud is Batman-like in terms of personality in more than one aspect - particularly that there are very few, if not no other, people who can get through to him like his soul mate - Aeris, of course, in his case - can. Does that make sense?