[CHz]

The game credits both HIYA! and JIM with sound, but the back does say "all music composed by" HIYA!. I'm not sure if Data Discs was actually in contact with him or someone else who would know for sure? HIYA! mentions having worked with JIM in the liner notes of the Metal Slug box, but doesn't say what he did.

FWIW the soundtrack sounds almost all like HIYA! to me