Japan and America are alarmed at Russia's military build up in the Far East. I think China is the real target.
In theory this should be a worry for America and Japan:
Russia caused a major stir earlier this month when it deployed one of its most advanced air defense systems, the S-300V4, on a disputed northern island claimed by Japan.
This was no isolated incident: For several years now, Moscow has been on a mission to strengthen its military presence in Northeast Asia. To counter the U.S., Russia has upgraded its weaponry in its Far East, commissioned new ships for its Pacific Fleet, and significantly expanded military cooperation with China.
If Russia is so worried about America and NATO, why would Russia move forces away from the heart of European Russia? Doesn't preparing for a virtually non-existent American-Japanese threat to the Russian Far East make Russia's western border--which the Russians bizzarely claim is under threat from NATO--easier to overrun?
But I don't think the Russian build up that I've mentioned here, here, here, and here, is a real problem for America and Japan. Russia just can't admit it.