za-i-ni-chi noun, plural, countable
Koreans being residing in Japan are referred to as Zainichi.
During the Japanese occupation of the Korean peninsula in the period 1910-1945, Zainichi came to Japan to seek a better life. They abandoned thier own country due to the Cold War between the United States of America and the Union of Soviet Socialist Republics or the Korean War broke out in 1950 although the General Headquarters in Japan ordered them to return to Korea in 1945.
Koreans living in Japan pretending to be Japanese. May or may not have been born in Japan. To the westerner's eye they appear no different from real Japanese.
Despite claiming to be "Japanese," zainichi have enormous Korean pride (like all Koreans) and will usually boast to you within a few minutes of first meeting that they are in fact Korean. They also use their Korean name whenever possible. In reality, they are no more "Japanese" than a Swede or Ethiopian who happens to be born in Japan.
They are infamous for running the mass media in Japan, the fake far right movement ("uyoku dantai") as well as controlling the yakuza criminal underworld (gambling, prostitution, drugs, etc.). Most "bad neighborhoods" in Tokyo and Osaka are actually zainichi neighborhoods.
American in Japan: "Hi! My name's John. I'm here studying the Japanese language. Nice to meet you."
Zainichi: "Hi John. I'm Korean. What are your hobbies? I'm Korean."