[1] During the Sengoku period, Tosa Province was dominated by Chōsokabe Motochika, who conquered most of Shikoku from stronghold at Okō Castle.

Although the new castle had the advantages of space and a central location, the area around the hill at this time was extremely swampy, due to the influx of alluvial sediments from the Kagami River, and was prone to flooding.

However, Motochika's successor Chōsokabe Morichika joined the pro-Toyotomi Western Army at the Battle of Sekigahara in 1600, and was subsequently deprived of his title, and later his life.

The castle is relatively small, as it was constructed primarily as a defense against possible rebellion by former Chōsokabe retainers, who were very unhappy with the death of their lord and the imposition of rule by the Yamauchi clan and Tokugawa Shogunate.

In addition to a tearoom, genkan (entrance area), and latrine, the Kaitokukan contains eight traditional rooms, ranging in size from three to twelve tatami.

The main gate of the castle located at southeast direction of the hill, and outer moat surrounded south half.

They contain the Prefectural Library and the Kōchi Literary Museum, in addition to statues of notable scions of the Yamauchi clan.