You can talk all you want about cross cultural ideas and relative genetic closeness and such, but I assure you, the Japanese and the Chinese are distinct and do see each other as distinct. To put it in a different analogy, I wouldn’t expect a story set in the Norman invasion of 1066 to star D’artagnan, and if it did—without a huge part of the plot being devoted to why and how—I’d assume someone fucked up.