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Cognomen 古屋 (Kashin , 古屋 , Коя ) , all around the world, is quite a rare last name. The cognomen 古屋 is characteristic of Estonia, where it is a rare surname, Russia, and Canada, where it is a very rare surname. Not in comparison with a country's population, the name is most common in Russia, India, and Nigeria. More prevalently, 古屋 is the forename as well as the last name.