If you want to modify any of the files in the "default" folder, copy it here and change them to your heart's content.

The game will check first in this directory, and if it can't find each file here, it'll look for them in the "default" directory.

The file called "music (proper songs)" has the approximate battle songs each character use in their respective series, place it here and delete the parenthesys if you want to use it. You'll have to get the songs on your own, though...