Japanese culture originated from Yamato nation dated back about 1500 years ago. Yamato nation used only "kana"language. In Nara period Emperor Shoutokutaishi introduced "kanji" from China. So Japanese language is a mix of "kana" and "kanji".
But Japanese culture is original, different from Chinese culture.Japanese ancestores aren't immigrants from Northern and Southern countries. Yamato nation existed after Jyoumon period. Recently archaeologists found the ancient tomb called "Hashihaka Kofun" proving the existence of "Yamataikoku".