What is the capital of Japan?

Tokyo is the capital of Japan and serves as the country's political, economic, and cultural center. It is the most populous city in Japan and is known for its blend of traditional and modern elements, such as ancient temples alongside skyscrapers and bustling streets. Tokyo is also home to the Japanese government, including the Imperial Palace and various ministries and agencies.

The other options are not relevant as capitals of Japan. Beijing is the capital of China, Seoul is the capital of South Korea, and Hong Kong is a Special Administrative Region of China with its own distinct governance, but it is not a capital city. Thus, Tokyo is the only correct answer for the capital of Japan.