Who appeared in Japan around 300 BCE?

Answer 1

The Jomon Period (13000 BCE to 300 BCE) ended in 300 BCE and the Yayoi Period (300 BCE to 300 CE). This period was marked by the introduction of rice and the parallel development of farming to replace the hunter-gatherer culture. This initiated social change such as the development of classes. There is some indication that Japan may have entered the Iron Age during this period. Towards tthe end of the period Chinese has visited Japan.

So the "who" that appeared in Japan would have been farmers, metal workers, landholders and potentially Chinese travellers.