South Korean government did not help Koreans living in Japan during hard times. North Korean
government isolated and poor they were 60 years ahead supporting Koreans living in Japan during economical and political hard times. Majority of 80 percent Koreans living in Japan are from Southern Province island " Chejudo". Koreans living in Japan do not like to divide political alliances between North or South because majority of them came from South Korea whereas to preserve Korean cultural identity they studied or supported North Korean government run schools.

Populations: If you combine all Korean populations in Japan. ( Main island plus Sakhalin island)
it would be about 1 million. ( Korean, Korean/Japanese ( mix), Korean/Russian (mix).