Baron was a samurai of late Edo period Japan who went on to become a noted general in the early Meiji period Imperial Japanese Army. An Aizu retainer famous for his ingenious strategies against the early Meiji government during the Boshin War to overthrow the Tokugawa bakufu, he was of the first people from Aizu to write a history of the years leading up to the war, together with his brother Yamakawa Kenjirō.