[4] Okō Castle was located on a 97-meter mountain at the northern edge of the Kochi plain, next to the Kokubu River.

The main road from this area to Awa Province passes this castle, making it a strategic location for controlling the movement of people and goods in southern Shikoku.

[7] His son Chōsokabe Kunichika narrowly escaped from Okō Castle and several years later returned by Ichijō Fusaie's help and recovered the clan's territories in the eastern part of the Kochi Plain.

[7] Kunichika sought revenge against the Motoyama clan, who controlled the western half of the Kochi Plain, and more importantly, the port facilities at Urato Bay.

Motochika defeated an attempt by the Aki clan to take Okō Castle in 1563 and by 1570 had secured control over all of the Kochi Plain.