In ancient times when the concept of demotion from nobility to subject was not yet clear, Imperial Families with ancestors from after the era of the ninth Emperor Kaika, were given the surname Kimi (Kabane).
臣籍降下の概念が明確ではなかった上代においては、第9代の開化天皇以降の皇別の氏族には公（きみ）の姓（かばね）が与えられていた。