Kim Jong-un’s mother was Ko Young-hee and she was born in Osaka, Japan from parents born on Jeju island. In an Asahi Shimbun article, Ko Young-hee’s Japanese origins are explored.
However, Kim Jong-un’s Japanese connections won’t play well with the myth makers in Pyongyang, the same guys who claim that Kim Jong-il was born at Mt. Baektu (he was really born in Siberia).
According to one Korean-Japanese North Korea expert, the story will likely follow this theme:
“Ko Tae-mun [Ko Young-hee's father] carried on the will of Jeju islanders who fought bravely under the guidance of Kim Il Sung. After fleeing to Japan, he returned to North Korea to be embraced by the greatness of Kim. Ko gave up his life to serve as a soldier for Kim. Kim Jong Un would be an individual who carried on the great revolutionary bloodline from Jeju.”