This article explores the origins and prevalence of the Kim surname in Japan and Korea, clarifying whether someone with this name is Japanese or Korean. While Kim is a rare surname in Japan that originated from the Ainu indigenous people, it is a prevalent surname in Korea that originated from the Gyeongsang Province during the Silla dynasty. The article also discusses cultural similarities and differences between Japan and Korea, as well as mixed heritage individuals and cultural appropriation. Ultimately, one's nationality and ethnicity should be based on family background, language proficiency, and cultural identity rather than just their surname.