The key identifying characteristic of this frame is the seat stay cap at the seat lug. You'll notice that it comes almost to a point, as though the tube was drawn down to a point. Early Azuki's and early Nishiki's had this seat stay cap design. I can't remember(doesn't mean they didn't exist)any other frames with this particular design.

Nishiki's with this seat stay design were the earliest Nishiki's I saw in this country, and I started seeing them where I grew up, in the midwest, around 75/76, but they were called Internationals then so this may be an earlier model. I have never seen or heard of a Kokusia before.

That kinda pearlescent color was also very distinctive to Nishiki/Azuki.

Someone made a comment about Kokusia meaning International. The International was Nishiki's mainstay model for a long time.