Typically the Roman-letter postmarks were applied to outbound foreign mail. I don't have anything handy to check the timeframe of this example against, but it doesn't jump out to me as odd, other than the foreign cancellation being applied to one stamp and the commemorative cancel to the other. (But perhaps that was either the maker's request or the post office practice at that time.)
These are, of course, the stamps that Japan issued to commemorate the 1st anniversary of their bombing of Pearl Harbor. (It was December 8th in Japan, because of the international dateline.)
Thanks, Philatarium. That's exactly the information I was hoping to get.
I collect/exhibit the Pearl Harbor stamp but have previously not seen the Roman-letter postmark on related covers. This is a FDC which doesn't appear to have actually gone thru the mail (no addressee). I suspect that was the maker's request.