In 1587, Toyotomi Hideyoshi confirmed the Sō clan possession of Tsushima. Yoshitoshi thus entered Hideyoshi's service; among the first major tasks he undertook on behalf of Hideyoshi was to organizing negotiations with Korea as Hideyoshi's representative.
In 1587, Toyotomi Hideyoshi authorized the Sō clan to govern Tsushima. Consequently, Yoshitoshi entered Hideyoshi's employ; one of his initial tasks under Hideyoshi's direction involved negotiating with Korea on behalf of Hideyoshi.