During the Kamakura era and the Muromachi era (1192 - 1575), groups of marine guards called "Iyo-suigun" appeared and came to dominate the vital supply routes in the Inland Sea between the western province and Kyoto, then the capital of Japan.

The ancient manuscripts tells of the activities of Kutsuna Family who led the Kutsuna Suigun. They were the one of the Iyo Suiguns. They had the privilege of knowing the navigation of ships and they taxed all the traders and Samurai worriers who tried to go through the channels.