Although before I do, I must add that I like the Stephensonian moniker.
1 and 2) I think what we’re dealing with here is the difference between balancing as a description of behavior intended to counter or neutralize visible threats to a state’s security and balancing as the process by which the structure of international system changes. Japan may be engaged in the former in regard to North Korea and the latter in regard to China. There may be some overlap, but perhaps not as much as meets the eye. (Although any legal or constitutional changes that grow out of the North Korean threat would undoubtedly influence balancing against China.) For example, Japan has little reason to ramp up military spending to neutralize the threat posed by North Korea. The debate is over whether passive or deterrent defense is adequate to meet the threat posed by North Korea’s missile and nuclear programs, or whether Japan needs to consider preemptive defense. Arguably meeting the North Korea challenge does not require all-out mobilization, a comprehensive change in how Japan mobilizes national resources in response to external threats. The debate over how to deal with the North Korean threat is obviously connected with the debate over how to deal with a rising China, but the question is how these two debates are connected.
One connection is simply that Japanese hawks are not making clear distinctions between North Korea and China when making their case. I figured that Waterhouse and I agree on the importance of China for Japanese balancing behavior over the long term, but my point was that China may play a more prominent role in Japanese debates about balancing in the near term than I read his post as arguing. After all, Waterhouse wrote of “the lack of bold, provocative military signals from China of late,” which may be true in an objective sense, but from the perspective of Japanese elites arguing for balancing behavior of one form or another, China has done plenty to merit more balancing on Japan’s part, whether by spending more on its military or by sending the PLA Navy to waters ever further from China (and by acting with greater assertiveness closer to China). Arguments about China may carry less weight than arguments rooted in meeting the North Korean threat, but some elites are making arguments about the China threat. It may not be easy to separate the two: national security hawks are trying to create a climate of uncertainty in order to sell their policies, and they are willing to use any external threat at hand to make their case. North Korea may provide a particular perturbation — but the sensitivity of elites and public to a perturbation may have as much to do with worrying signals from China as with North Korean behavior.
3) Just to build on a point here, there are a number of different ways to think about post-cold war changes to the US-Japan alliance. External balancing against a long-term threat may be the most likely explanation, but there are other plausible explanations, whether domestic politics or a structural explanation rooted less in preparations for a rising China than in the impact of unipolarity of the US alliances that were the legacy of the cold war. It is entirely possible that we may be entering a period in which Japan chafes at a security policy overly centered on the alliance and instead opts for Samuels’s “Goldilocks consensus,” a grand strategy that features a more even mix of external and internal balancing, maximizing Japan’s options in a changing regional security environment. (Of course, if US power declines markedly relative to China’s, structural realism would presumably predict greater incentives for external balancing by both the US and Japan and more internal balancing by Japan to compensate for US relative decline.)