From a well-placed military research guy:

Jonah:
Japan is classified as a “Virtual Nuclear State”. They have developed a complete nuclear fuel cycle (including plutonium breeding and extraction) but have only refrained from developing nuclear weapons because of the cultural stigma involved. North Korea’s antics over the last decade have been eroding this cultural taboo at an ever-increasing rate. Serious analysts of Japan’s nuclear industry argue (including a very senior member of the National Security Council) that Japan could go nuclear within six weeks of deciding to do so.
Also, Japan has several delivery systems, including a orbital rocket that could be developed into an ICBM rather quickly.
Fear is a dangerous thing. Especially when you are a couple of hundred miles from a madman.