Born in Nihonmatsu, Japan, Kodama lived with relatives in Japanese-occupied Korea early in his life, and during that time formed an ultranationalist group with the intent to assassinate various Japanese politicians. He was caught and served a prison term of three and a half years. Kodama used his power in the yakuza to suppress anything he deemed the least bit communist or anti-nationalist. In 1947 he ordered the Meiraki-gumi, an affiliated gang, to break up a labour movement at the Hokutan coal mine. He also offered his support to the anti-communist right-wing Liberal Democratic Party.