When people from mainland China populated Japan, China didn't exist. So it's not a colonialization from people of one country to another. Otherwise, we are all africans.
Actually, that's wrong. There is actually a trace, specifically. The earliest Japanese civilization (State) traced its lineage to the King Taibo of the State of Wu. The Yayois of Japan (Sinic Race) trace ancestry to the State of Wu. This was 4 centuries before the contact between Emperor Guangwu of the Han Dynasty and his Japanese contemporary.