That's not true. You need to go way way back to time before China and the Han Chinese. Way back into history and ask yourself who planted the seed for all the branches? They aren't the original but we do branches off. Japanese are Japanese because they think differently and their believes are different. Different beliefs build different ppl.
The Japan and Japanese that you know and see is a product of Han Yayoi migration into what is now the Japanese Archipelago. The mingling of Han and Koreans, actually. With them, the Han brought bronze culture , and high civilization that transformed the landscape. Everything you see in Japan --- is years, thousands of years, of cultural accumulation by way of China and Korea (more so China).
Yes the identity of Japanese are their own, but because of deep Chinese influence (genetic and cultural), Japan we know of today exists.
This is why we Japanese have a mixed and sensitive issue with China. Japan cannot belie China as we know we come from them, and as much as politics plays politic, Japan (and Japanese people) need China (and Chinese people).