[1][2][3] Following Toyotomi Hideyoshi's conquest of Kyushu of 1586-1587, he assigned Tachibana Muneshige as castellan of Yanagawa Castle with a fief of 132,000 koku.

Yoshimasa vigorously carried out the maintenance of the territory, such as renovating the Chikugo River, encouraging the development of new paddy fields, and building a 32-kilometer embankment on the coast of the Ariake Sea.

The former Tanaka territory was divided, and Tachibana Muneshige, who had managed to receive a pardon, returned to Yanagawa Castle with an increase in kokudaka to 109,000 koku.

In addition, in the following year (1621), Tachibana Tanetsugu, a nephew of Muneshige, entered established Miike Domain with a kokudaka of 10,000 koku.

He also made efforts to introduce Western-style guns in his military, and participated in the First and Second Chōshū expeditions on the side of the shogunate.