[HELP]: mystery theme from "203 Kochi" (二百三高地) or Battle for Port Arthur -- trailer -- 1981
After finding this gem of a movie a few days ago, I returned once more to the trailer (posted on Youtube) to leave a comment and thus began my search to find the name of this catchy mystery song. I backtracked through popular Japanese music charts from the 80s, before and after the release date to see if perhaps one would match, but to no avail. As I do not speak Japanese, I turn to Reddit for assistance. Does anybody recognize the trailer's theme?