Going to post a bit of classical music; I have particular pieces I half-associate with every arc except Emi's (still working on that one).
Hanako: Chopin Ballade #4
Corresponds pretty well with my rather dark view of Hanako's arc (esp. after bad ending).
Rin: Ravel Ondine
Quite amorphous/abstract, consistent with her arc. It's always moving around and jumping from place to place and you can never put your finger on exactly what's happening. Also one of my favorite pieces in general.
Lilly: Ravel Concerto in G, Movement 2
A somewhat simple-seeming piece and yet so incredibly beautiful anyway, paralleling how I felt about her arc. It also has the almost-dreamlike feel that the latter portion of Lilly's arc has, at least for me.
Shizune: Ravel Concerto for the Left Hand
So powerful in some places and yet so unexpectedly vulnerable in others. Of the four this is the piece that is most strongly connected to the arc in my mind.
And yeah, I have a massive bias towards Ravel; oh well...