According to newest researches, rice originated from the Lower Yangtse region around 9,000 years ago, whereas Yunnan, Guizhou, and Guangxi in the extreme southwest of China only entered agricultural age around 4,000 years ago. Hence the rice agriculture did not come from those regions.
Sorry, but your claim that Japanese originated from Yunnan isn’t supported by genetics and archaeology. Neither Jomon nor Yayoi are close to South Chinese minorities and SE Asians on autosomal PCA charts. And archaeologically Japan had close ties with Korea and Northeast China.