From Dean's Journal:
...Japan has clear superpower potential. With North Korea flexing its muscles, and the ongoing dispute between Red China and Taiwan threatening stability and the sea lanes, it's almost amazing that Japan has restrained itself up to this point.[...]
Should Japan be pushed to the point where it feels it needs to use all the military power it is capable of generating, it could readily become a superpower in military terms. Its tradition is of a highly-trained, professional force that can be a fierce adversary (as it demonstrated during World War II) would be there, and this has long worried Japan's neighbors. The only reason Japan is not a superpower is because it has chosen not to pursue that course.