Chikayasu was the third son of Chosokabe Kunichika and a younger brother of Chosokabe Motochika. He was adopted by Kosokabe Chikahide in 1558 and following the defeat of the Aki family in 1569 was given Aki castle. He went on to serve Motochika loyally throughout his career. He played a notable role in the Chosokabe victory at the Nakatomigawa in 1582 and captured Tsu castle, afterwards being given Tomioka castle in Awa province. He was known as a diplomat as well as soldier, and worked at arranging a Chosokabe-Oda alliance. He sent messages to Oda Nobuo and Tokugawa Ieyasu when the latter two were facing Toyotomi Hideyoshi in 1584. After these endeavors, his talents became widely known. He died of illness in Nagato province en route to join the Korean Campaign in 1593. His eldest son Chikauji had also died of illness the previous year. A younger son, Sadachika, left Tosa province following the Sekigahara Campaign and settled in Shimôsa province.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005