Japan is not. According to UN documents, Japan is not allowed to own any territory beyond its own four islands.You just remind me that Japan is another country which has wit territorial disputes with every single neighor, namely Russia, China, North Korea and South Korea.
The current dispute is only about the United States stirring up antagonism between Japan and its neighbors to prevent Japan from reconciling with the rest of Asia. By the time the United States returns to United Nations rules, Japan will have no territorial disputes.