The characters in question:
-Lilly
-Hanako
-Shizune
-Misha
-Rin
-Emi
-Kenji
I just can't find anything good for Hisao, so no Hisao.
(and if you feel so compelled, I suppose you could throw in the minor characters as well)
I'll start:
Lilly: The Stars Come Out, by Brother Android.
From Brother Android's awesome, free "OctNovDec", an album about autumn and nature.
Lilly doesn't treat her blindness as a disability, yet I can't help but imagining lying with her on a grassy hill somewhere in the solitude of Hokkaido as the stars come out, trying to find the words to describe them to her. Stars are an object of fascination for me, from a philosophical perspective. In turn, it inspires a lot of emotions just thinking about her not being able to experience that.
Those feels. Those feels.
Hanako: Needles, by System of a Down.
This is a song about drug addiction (on the surface, anyways), but it's also a song about being controlled by (and breaking free of) something that comes from within. I don't know if the right word to describe Hanako would be that she is "controlled" by the trauma of her experience, but in a way I feel she is very much trapped by it, and throughout the path we see her break free. Also, it's accompanied by a pretty intense sound, and I imagine Hanako feels pretty intense on the inside.
Shizune: First Friday Funk, by Flying Lotus.
Obviously, Shizune's experience with music is going to be fairly limited. I have the feeling that she would at least be able to find an interest in the throbbing bass of Dubstep (real Dubstep, guys like Loefah and Digital Mystikz, not that Skrillex bro-step crap). Not being deaf, I can't tell if somebody could really interface on that level with the vibrations, but I think there's something to it. Anyways, First Friday Funk (which some of you might recognize from Adult Swim) is a song that I feel strikes very deep emotionally, just by virtue of its sound, and it just reminded me a lot of Shizune's path, for some reason. So, yeah.
Misha: Mood Swings, by Swindle.
Alternatively, Bizarre Love Triangle, by New Order, for fairly obvious reasons
Shizune path spoilers:
The Misha of Shizune's path gives us an entirely different perspective on the character than those of the other paths, in which she is more or less revealed to be this seething mass of emotion and depression, well concealed by her bubbly pink surface. I felt that the song reflected that hidden nature very well, with its relatively upbeat exposition dropping into dark oscillations.
Rin: Duel in the Deep, by Lightning Bolt.
Duel in the Deep is the sort of "song" that, at first, doesn't make much sense. It is best described as bizarre, at first glance beyond immediate comprehension. But one night, letting Lightning Bolt's excellent "Wonderful Rainbow" album play on a loop, it just sort of made sense. The circumstances were right, the catalyst was apparently present, and everything fell into place. What was once strange and otherworldly was suddenly evident. I feel that Rin is a lot like that.
On a different note, I think she'd appreciate the raw, alien nature of the sound. It's said that she enjoys this sort of weird music, after all.
Emi: Running, Jamie xx's rendition of Gil Scott-Heron's incredible poetry.
It's all in the lyrics - just give it a listen, and I think you'll be as amazed as I was at how well the lyrics sync up with KS's portrayal of Emi.
Kenji: Stone Cold Crazy, by Queen.
Not only is Kenji pretty crazy, but the song's theme of escape, tension, and paranoia fit Kenji pretty perfectly, in my opinion.
Your turn.
