This is a provocative move by the North Koreans, and we learn that Prime Minister Aso's reaction was:
"The prime minister stopped short of demanding further U.N. sanctions if North Korea goes ahead with the launch."
All he can do is say: "If you do this, I might think about telling the UN." We know from experience with Iraq and Iran, that the UN means nothing to a country like North Korea. The sad reality is that Japan can't do anything. It doesn't have the military, economic or political muscle to do a single thing.
China, now that's a different story. If China wanted North Korea to back down, they could do it.
Another sign that Japan is fading into Geo-political irrelevancy.