The anxiety was not limited to Japan either. The US--and, I assume, others--was made very nervous by the prospect of a reunified Germany.
In terms of Japan, that sounds more like an issue with the economic growth of Japan during the latter years of the Cold War. From what I've read, the Japanese economy was supposedly on track to surpass the US economy. The general consensus was that Americans should learn Japanese. The Japanese economy took a significant downturn throughout the 90s and have had mostly stagnant growth since. However, Japan is still the 3rd largest economy in the world and a country that punches far above its weight.
Japan's stagnant economy in the 90's was also due to low birth rates. China is facing the same demographic problems Japan did in the 90s.That may be true, but the downturn in the Japanese economy coincided with the end of the Cold War. I haven't heard of anyone that says the two are related. Even now, Japan is quite secure as the 3rd largest economy in the world. The US and China are far ahead and Germany, the 4th largest economy, would have to grow almost 25% at the expense of Japan. When you look at the world's largest economies, the world order is barely changed since the early days of the Cold War, with the major changes being that China has replaced the Soviet Union and that Japan has grown massively.
Japan can be a powerhouse once again if Article 9 is repealed or amended. I think we need extraordinary measures to contain China and I think Japanese remilitarization is the most important start. I would argue for nuclear weapons in Japanese territory under US authority, if that is what the Japanese would like.
