This article focuses on a seven-year legal battle initiated against the Japanese government in the 1970s by a South Korean illegal entrant and its historical significance. Son Jin-doo, a victim of the atomic bomb dropped on Hiroshima, demanded the Korean hibakusha receive the same medical and legal rights that the Japanese hibakusha had been granted since 1957. His legal case contributed to bringing Japan’s long-forgotten colonial past to the surface and raised the question of why many Koreans resided in Japan during the colonial era. Additionally, the trials revealed the different legal statuses of Japanese hibakusha and overseas hibakusha. Son Jin-doo was a pioneer in asserting the rights of the latter and raised consciousness about the abandonment of the Korean A-bomb survivors.