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. 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. Kunichika began by seizing Nagahama Castle, a branch castle of the Asakura clan who were allied with the Motoyama in 1560. This marked the battle debut of his son Chōsokabe Motochika. On hearing of the fall of Nagahama Castle, the Motoyama responded by sending 1000 troops in a counterattack. Although the Chōsokabe had only 300 men, the fierce resistance led by Chōsokabe Motochika foiled the Motoyama attempt to retake the castle. Chōsokabe Kunichika died shortly after the battle. 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. By 1575 he had expelled the Ichijō clan and had united Tosa Province under his rule. Chōsokabe Motochika then invaded Awa and Iyo provinces, which he conquered by around 1580. Motochika was allied with Oda Nobunaga, but after the latter's assassination in 1582, he accelerated his campaign and had taken almost all of Shikoku by 1583. However, Toyotomi Hideyoshi viewed the Chōsokabe as an increasing threat and launched an invasion of Shikoku, decisively defeating the Chōsokabe at several locations, and limiting their rule to Tosa Province. Motochika moved the clan seat from Okō Castle to Urato Castle in 1591, and the castle was abandoned by 1598
