For my last few long projects, I've associated music / soundtracks with them in one way or another, whether it be assigning each character a song as I wrote up profiles, or - in the case of Scylla and Charybdis - coming up with a concept list during the writing process. Generally speaking, even those projects where it is a song (or songs) per character, I also have some that encompass wider aspects of the story.
I'm currently building a list for Surgeburnt - building in that my ears are still peeled for songs to reference specific characters or combinations. This was my first pick for overarching thematics and still tops the list:
Sum Of Our Parts
I keep trying to pick out specific lyrics to highlight, but the whole thing, from lines to atmosphere, fits perfectly.
Check out the alternate version, as well. Mary Lambert is amazing, and I am mostly irritated that she doesn't have a second CD out yet (come ooooon already).