The United States guarantees Japan access to its raw materials. But Tokyo sees the American concern in Russia and the Middle East as potentially dangerous to Japan's ability to access what it needs. A war that closes the Strait of Hormuz would cut Japan off from its supply of oil. Washington, from the Japanese point of view, is prepared to take risks that are minor to the United States but potentially disastrous to Japan. Tokyo's fear is that the United States will act not against Japan, but against a country on the road to a country Japan needs, heedless of the consequences to Japan.
The Japanese are quite aware of the problem, as well as that there is no way to limit this risk apart from staying close to the United States. Tokyo is also aware that the more problems the United States has with China, the more thoughtful Washington will be with Japan. But the United States has a queue of problems, and China, rhetoric aside, is not one of them. Whether it gets there will have less to do with what Beijing intends than with Beijing losing power over parts of China. That would draw the United States in and give Japan the leverage it needs.
But that is, as I have argued, a possibility for the future. The internal evolution of China is, in fact, the key to the region. China has moved from limited liberality to increasingly intense authoritarianism. The evolution of this government is at the heart of the East Asian dynamic. North Korean nukes, Chinese aggressiveness at sea and American threats are all secondary.