I went back and checked the database. Unfortunately, not everybody with your code format provided pictures but for those that did, the serial number was on the under side of the bottom bracket shell.

Your frame is semi-aero style, in that the seat and tubes are not aero profile along their entire length. They are aero profile in the middle and round at the ends. This is a cost concession to permit the use of conventional lugs, standard front derailleur clamps and round seat posts. I've only see a handful of Shogun aero bicycles and none are an exact match for yours, though the the stay cap treatment is similar.

You also mentioned the possibility of an SR. I have one serial number for an SR aero frame in my database and it is definitely from a different manufacturer.

The bottom line is that I can't tell you which brand your bicycle was marketed under. The S/N format is consistent with that of a Shogun contractor but I haven't seen an exact match. About all can say is that it was manufactured in Japan in 1981 and late enough in the year that it could be a 1982 model.