I don't think that Japan will ever join the Shanghai Cooperation Organisation. The SCO is primarily a Sino-Russian alliance, and Japan is not in good terms with both these nations. Also, as long as they remain as an important ally of the NATO, they are not going to have any tie-up with either Russia or China.
Technically and happily Japan has no tie to NATO but ONLY AMERICA. Soltenshit has no say over Japan. Technically those different are very artificial in nature. Once integrated in the SCO the fish island become a mute point as the kurils. Both are solvable. It will not change the life of both nations what the extractive potential that there are it will not make an inch of a difference for a power like Japan... We aren't speaking about the Philippines (triggerfishing
).
Edit: for China It's a question of principle. What belongs to China will return to China. All nations that have exploited an opening in a chinese transitions across history have all paid an heavy price. And as you can see, all those "opening" never were mortals. Most of the time necessary to reach the next stage.
But thank you for your comment. I really appreciated it.
