The maritime clans of Japan originally went by the name kaizoku, sea tribes. In other words, pirates. Later they were promoted to suigun, naval forces, when their usefulness became apparent to the land-based clans who wrote the histories of Japan. As with its English equivalent, kaizoku is pejorative, reflecting the contempt in which they were held, and the fear that they inspired. In reality, they pursued the same path to power as Japan’s land-based clans, but with the sea as their main field of operations. From armed brigandage they proceeded to warlordism, thence to local government and eventual incorporation in the nation state as the Japanese navy.

The Kōno clan originated in Hōjō, now part of Matsuyama. In the Genpei War (1180–1185) between the Taira and Minamoto clans, the Kōno allied with the winning Minamoto. When the Minamoto established the Kamakura shōgunate, the Kōno became their retainers, and as the shōgunate’s deputies in the west of Japan, their power grew.

In the Muromachi period around 1340, the Kōno transferred their base from Hōjō to today’s Matsuyama, where they built Yuzuki Castle in what is now Dōgo. For a while, the Kōno family commanded the Kōno Suigun, the largest naval force of the Setouchi region. The main shrine of the Suigun of Iyo was Ōyamazumi Shrine on Ōmishima island, and it was their habit to go and worship there. If they met with success in battle, they deposited their arms as tribute to the gods. Consequently, the Treasure House of Ōyamazumi Shrine is today one of the largest repositories of historical weapons in all Japan.

During their long history, the Kōno experienced many ups and downs, sometimes making poor bets on patrons beyond their power base. During the Kamakura period, the fortunes of the Kōno declined following their support for the Retired Emperor Gotoba. However, during the second of two Mongol invasion attempts against Japan in 1281, Kōno Michiari made a name for himself as a bold leader, after which the Kono clan enjoyed the peak of its prominence.

After praying at Ōyamazumi Shrine, Michiari sailed with his forces to Hakata in Kyūshū and made his camp on the beach in front of the defences to the amazement of all. Inspired by the sight of a white heron flying off with one of his arrows, Michiari led his small kohaya boats among the enemy, dropped their masts onto the biggest ship in the fleet and climbed up it. They captured a Mongol general and gained military fame. A painting of the white heron can be seen at Ōyamazumi Shrine today.