Oh is the son of a Chinese father (from Zhejiang) and a Japanese mother and was born in Sumida, Tokyo, Japan. He had Japanese citizenship when he was born because Taiwan, his father's home, was part of the Empire of Japan. After the end of World War II, control of Taiwan was given to the Republic of China (ROC). Taiwanese people were converted from Japanese citizenship to ROC citizenship. Until January of 1985 the children of a Japanese father inherited Japanese citizenship, but if the father was not Japanese, the child was not Japanese. This changed on January 1 1985. This was a big problem for Oh as a youth: he speaks Japanese and has lived in Japan all his life. He and his three daughters hold Republic of China passports.