The Ōu Honsen (奥羽本戦, Main battle of Ōu, a pun on the Ou Line railroad traversing the prefectures) is a footballing rivalry played between Blaublitz Akita and Montedio Yamagata, both professional J.League teams from the cities in the former Dewa Province, Japan. It is also known as the Dewa derby or Chokaisan derby, and named after Japan Railways Ōu Main Line which connects Akita City and Tendo, Yamagata. Series winners can wear home kits at the opponent's stadium next season.