As much of Hiro Watanabe’s message consisted of characterizations about what his first message was or was not, and what he actually meant to say, I will defer to him and to other members of this forum to determine what his first message was about. In addition, I will continue to avoid his points that range far from the main discussion, such as China’s supposed lack of soft power (I address this in part in an upcoming co-authored article in International Studies Quarterly), or the (mis)reading of Paul Kennedy.

“As for Midford's reference to the Sino-Japanese alliance, I still have to say that it is unrealistic and most Japanese and Chinese would consider it outrageous.”

I don’t know to whom this is addressed. I don’t think anyone is suggesting that PM Noda suddenly propose a Sino-Japanese alliance out of the blue, which given the current relationship probably would cause many Japanese and Chinese to view it as “outrageous” (although reactions would undoubtedly vary along a continuum).
As I explained in my response to Ellis’ thoughtful comments, Japanese perceptions of China have varied widely in the post-war era, with levels of Japanese affinity toward China at the beginning of the 1980s matching those toward the US today.

Also, we have to think about Japan’s alliance options not in terms of the situation today, but beyond five years when China is projected to overtake the US in GDP, or when the US is no longer militarily dominant in the Western Pacific. Wishing thinking as a way to avoid these very real possibilities, i.e. by betting on China collapsing or assuming the US will always be dominant, is the intellectual equivalent of putting one’s head in the sand. I don’t pretend to predict the future, but based on what we know today these possibilities cannot be wished away.

“Midford mentions that it was uncertain if the US-Japan alliance would work at the time of its inception, this alliance is very different from the (unrealistic) Sino-Japanese alliance, so he cannot compare them.”

Again, a vague characterization is a poor substitute for a clear argument with concrete examples.

“By saying 'serious consequences' in the case of the termination of the US-Japan alliance, I mean a likely amendment to the Constitution (especially the abolition of Article 9) and rearmament (creation of offensive forces instead of the maintenance of self-desense forces only). …. it is most likely that Article 9 will also be amended if the US-Japan alliance is terminated, as Japan would have to defend itself”

Again, Japan already defends itself, and as such, it is not clear why Japan would have to change Article 9 or acquire larger offensive capabilities.

“China is likely to respond to this situation by increasing its military forces to a vast extent and acquire a more aggressive stance towards Japan”

As an end to the US-Japan alliance would significantly improve China’s security situation by parrying the potent US threat, it would have every incentive to accept Japan having a robust territorial defense, especially as Japan is no longer a candidate regional hegemon regardless of how pessimistic one wants to be about what sort of regime it might have in the future.
In this context, an alliance would give China leverage to ensure that Japan did not become hostile while giving Japan the same leverage vis-à-vis China. Japan entering an alliance with China would give China face in the eyes of Chinese nationalists while simultaneously ameliorating threat perceptions of Japan, just as the US-Japan alliance had the same effect on the US and its views of Japan. It is also worth noting that some Chinese foreign policy scholars are arguing that China is already becoming more accepting of a Japan with a robust defense capability (see Jianwei Wang’s chapter in the new Soeya, Tadokoro and Welch volume on Japan as a Normal Country).

“Given the nature of education which does not promote discussion or leadership skills and the existence of language barriers, Japanese individual politicians are likely to find it difficult to be assertive or influential at international venues.”

I would argue that Japan has long exercised leadership in international venues. Also, there are different styles of leadership: e.g. national level initiatives versus the quiet consensus building model that is more typical of Japan and ASEAN.

“Agency and ideas matter in addition to institutions.
However, in the case of the US-Japan alliance, institutional constraint is much greater than Midford recognises. The US-Japan alliance has been an essential part of the international security relations of East Asia. We need to identify the strong incentives for political actors too if we want to argue the possibility of dismantling this alliance.”

All of my posts have been precisely about this:
identifying some of the incentives that Japan might have to consider other alliance options, albeit without claiming that these benefits necessarily outweigh the ones Japan receives from its alliance with the US.
Again, the above is a vague argument: what are the institutional constraints? How difficult would it be to replace them with equal or better institutions? How flexible are the existing institutions? Can they really adapt to a region that is experiencing major shifts in the balance of power and other changes without becoming atavistic?

“I said that Japan would not be able to avoid the international outcry if it goes for a nuclear option.”

That depends on the state of the NPT at that time. The reaction in East Asia would likely be severe; although that would have to be balanced against the deterrence gains (just as Japan would not challenge a nuclearly armed China in territory it controls China would exercise the same restraint vis-a-vis a nuclear armed Japan, although it already largely does so anyway).
Also, China would be less opposed if there was a Sino-Japanese alliance or strategic rapprochement.
India’s going nuclear provoked an international outcry as well, and would provide a good model for broader international reaction. The biggest loser of Japan going nuclear would be its civilian nuclear exports, which is why Japan’s nuclear industry has been so opposed to this prospect.

“Finally, although Midford says 'there is no reason for believing that the US alliance serves as a real cap in the bottle holding back a resurgence of Japanese militarism', the end of the alliance is likely to strengthen hawkish opinions in Japan at least, if not necessarily leading to the resurgence of Japanese militarism.”

I have to thank Watanabe in being candid in acknowledging he is, more or less, an adherent to the cap-in-the-bottle theory.

“It is also important to understand that, during the LDP regime, Japanese right-wing extremists were not necessarily feeble but had certain influence by maintaining connections with some LDP politicians.
It is also a taboo and dangerous in Japan to criticise or ridicule the Imperial family in public (as on TV), as it is quite likely that one will be attacked by these right-wing extremists (An assassination attempt of Nagasaki mayor in 1990 for his claim of Emperor's responsibility during WWII is a good example. LDP was also criticising the mayor's claim). This is a very different situation from, say, Britain.”

All of that adds up to little beyond a feeble right-wing, even during the LDP regime. Isolated acts of violence related to the isolated issue of what is defamation of the Emperor do not translate into general political influence. The right-wing in Japan has never demonstrated influence over foreign policy. I will defer to others who know Britain better than I do, although the British comparison seems a bit overly idealized. Certainly in the case of the US, right-wing violence seemingly supported by the statements of elected officials is anything but unheard of. The Oklahoma City bombing or the Branch Davidian cases were, in terms of violence, an order of magnitude larger than anything the post-war Japanese right-wing has ever carried out. Nonetheless, none of these rightwing groups stand much chance of gaining political influence in the US either.

Paul Midford