The descendants of tozama Sō Yoshitoshi (1568–1615) remained at Tsushima-Fuchū Domain (100,000 koku) in Tsushima Province until the abolition of the han system.

He was rewarded for his victory with the post of Jito (local land steward), by the Shōni clan, shugo (governors) of Tsushima.

Though now holding the hereditary post of shugo of Tsushima, the clan remained vassals of the Shōni until the late 15th century.

From roughly the 1430s to the 1550s, the clan worked towards independence, its sights set on gaining true control of Tsushima, and on establishing friendly relations with Joseon Dynasty Korea.

[4] The Sō were required to greatly reduce the number of pirate attacks on Korea, and in return would be granted a virtual monopoly on Japanese trade with their neighbors on the peninsula.

This would later lead to the emergence of the Sō as one of the major clans in Japan, their wealth and power from trade more than making up for their small territory and submissive position vis-a-vis Korea.

[5] The Sō clan submitted itself to Toyotomi Hideyoshi in 1587 and supplied troops for the Japanese invasions of Korea (1592-1598).

After the abolition of the han system in 1871, the last known head of the clan, Sō Shigemasa (Yoshiaki), was made Governor of Izuhara Prefecture (Tsushima, renamed).