This could get very "interesting" ...
This is part of a current "trend" that deserves watching. China has similar disputes with Vietnam, S. Korea and, naturally Taiwan. Some of those disputes have the Philippines, Indonesia and Malaysia with additional claims in some of the same areas.
Japan has a PR problem that the U.S. should help it get over. It has been a very good business partner with many Asian nations for over thirty years now. They have all prospered because of the Japanese economy and Japanese investments. Japan has not been an economic bully and its direct foreign aid is the largest in the world. In spite of that, close cooperation with Japan on national security issues is still hard for many Asian nations to achieve. Neither they, nor Japan apparently, can get over the Japanese legacy of WWII. The shame is that Japan today is not the Japan of the WWII era. They need to have a stronger military that is part of cooperative security measures with its Asian partners.
We (the U.S.) need to work agressively for Southeast Asian cooperation with Japan on security issues. It would be in Asia's, and our, best long term interest.
Maybe we are. Bush's people have indicated that one U.N. change they would support would give Japan a seat on the Security Council. I support that. If India and Pakistan would lay down their sabers, completely, permanently I would support a joint sub-continent seat for them as well.
China is drunk on its own power. It is forcing Japan, Australia, the Philipines and even Vietnam toward a common purpose, namely, checking Chinese power in the region. If I were China, I would not want to see a militarized Japan.