Nagayasu Sogo was born in Sanuki Province of Shikoku, which was an island located in the Inland Sea. Nagayasu was the son of Sogo, the head of the Sogo clan from 1545 to 1565. Nagayasu Sogo was an adept warrior, leading his father's armies alongside him. He fought against the Kono clan and the Miyoshi clan, with limited successes. He was, however, also unfriendly with the Chosokabe clan, whose leader Motochika Chosokabe was expanding his clan's influence across Shikoku, conquering the Kono clan.
Nagayasu was the daimyo of the Sogo Clan from 1565 to 157, after his father died. In 1568, he went to war with the Chosokabe clan, who invaded Sanuki. Sogo led the defense of his family's castle, and won a costly victory over the enemy forces. Nagayasu was hailed for his power and his bravery in the battle, but the Chosokabe returned again a few years later and laid siege to his capital. Nagayasu was killed, a soldier chopping off his head. His soldiers collapsed, and Sanuki was taken and the Sogo taken down.