 In 1631, Komatsu inherited the Hoshina family headship, as well as the Takatō fief, and changed his name to Masayuki.Later recognized by his father and by his brother, the third shōgun Iemitsu, he was able to wield great influence in political affairs, and was to consequently see his income rating rise sharply.Masayuki became lord of the Yamagata Domain and was then moved to the Aizu domain (Mutsu Province, 230,000 "koku"), and founded the Aizu-Hoshina line (known from his son's generation onward as the Aizu-Matsudaira) which was to remain enfeoffed there until the Boshin War.