Thanks! The music came from a resource pack of royalty-free music. I'm uncertain of which specific pack at present, though.
Viewing post in Valkyrie: Sacred Feathers S comments
I guess it's possible that you bought a different version of the pack than I did, so maybe your EULA is different than mine, or something. But assuming that your EULA is the same as mine, it should be around the bottom of page 2:
2.3 Your game must include additional documentation that clearly indicates the use of the Resource Pack and the following copy:
[Copyright](C) Bitter Sweet Entertainment, Inc.
Published by: Degica Co., LTD
Resource creators: Bitter Sweet Entertainment, Inc.