The Ainu, their cousins, lived on the Siberian coast and moved into more Southerly areas as the Emeshi were incorporated within Japanese society as the military component we know as the Samurai.
The Yayoi, to confuse and confound all analysis, are composed of two and maybe three different groups of Chinese from very different areas. All arrived in Japan before writing systems were widespread in China ~ and we know that because it was not until the arrival of the Koreans in the 500s that writing became known in Japan (as well as Buddhism).
The work on the Hakka, one of the Chinese components, has been done by Chinese themselves ~ kind of hard to find interesting stuff about them so you have to look for "Great Wall" in any searches. The Hakka are the folks the Han supposedly built the wall to keep out!
Didn't work. Anyway, the Hakka raised wheat. The other Chinese raised rice. Both moved to Japan pre AD.
I'm not sure who the settlers were who brought chickens, but they brought an interesting breed that with a little selection can grow enormously long feathers. Always wanted one of them.
Yup. The Hakka are an interesting group. They moved all the way across China (five major migrations) and to this day are known as the 'guests.' They apparently originally had some Caucasian features as there are records that indicate severe persecution and even death for those with such features during the migrations.