According to Hitetsu, Kozaburo is a legendary master swordsmith whose craftmanship was known far and wide. His known masterpieces being two of the 21 O Wazamono swords Wado Ichimonji and Enma, the latter of which forces the user to use large amounts of Busoshoku Haki.[1]
History
Kozaburo constructed the swords Wado Ichimonji and Enma, which were classified as O Wazamono Meito. Over 50 years before the present day, he illegally left Wano Country.[1]
Trivia
His name is very structurally similar to Koushirou, a native of Shimotsuki Village, Kuina's father, and Roronoa Zoro's teacher; both names begin with Kou and end with rou, and contain a number in the middle: zabu meaning three and shi meaning four.