During the Nanboku-cho period, the Rusu sided with the Southern Court and pledged fealty to the Chinjufu shōgun Kitabatake Akiie.

In 1569, Rusu Masakage moved his seat from Iwakiri to nearby Rifu Castle, after having suppressed a local rebellion by the Muraoka clan.

Rusu Masakage went on to become one of Date Masamune’s senior generals, and was eventually given a fief at Mizusawa Castle, where the clan remained until the end of the Edo period.

The eastern bailey is the larger enclosure, measuring approximately 80 meters in diameter, and housed the main residential area of the castle.

Along the western line is a gentle slope up the hillside, with many small enclosures separated by dry moats and clay walls to prevent intrusion by an enemy.