Are Japanese a mixture of Han and Manchu?

There is a fundamental mistake in your cognition. That is, before all civilizations appeared, there could be no aborigines on the island of Japan. During the ice age, human migration spread over a large number of islands, and an island as big as Japan could not be empty.

Many mainlanders fled to Japan in ancient times.

There was an era in Japanese history, the Yayoi era, when there were a large number of people from the mainland, which made Japan enter the era of civilization.

These are not only Han people, but also Koreans and Mongols.

By the way, Manchu is only a branch of Tungusic language family, and in most cases it refers to Ewenki, not Manchu. There are Tungusic peoples in eastern Russia and northeast China.

Therefore, it is meaningless to say that the Japanese are the fusion of Han and Manchu. Just like some Korean scholars say who is Korean,,,,