Lifespan: Unknown to Unknown
Other Names: Genshichirō
Title: Governor of Awaji
Clan: Awa-Satomi → Awa-Masaki
Lord: Satomi Yoshiyasu → Satomi Tadayoshi → Naitō clan
Father: Masaki Yoshiyori
Siblings: Satomi Yoshiyasu, Tokishige, Satomi Tadashige, Satomi Yasutoshi, Yoshitatsu, Tadakatsu, sister (wife of Okudaira Tadamasa)
Masaki Yoshitatsu served as a bushō during the late Sengoku period. He was a member of the Satomi clan of Awa Province.
The Masaki were an illegitimate branch of the Miura clan. According to genealogical records, the family descended from the Sagami-Miura although there are assorted theories regarding their origins. During the Sengoku period, the family was active in the area around Edo Bay and the coastline of the Bōsō Peninsula, engaging in naval operations and commerce. The family served as senior retainers of the Awa-Satomi, a sengoku daimyō family based in the southern portion of Awa Province. The Masaki received a daughter from the Satomi, forging a blood relationship. Owing to the close connection between the Masaki and Satomi clans, the Masaki were similarly viewed as sengoku daimyō while in fact were sworn partners of the Satomi.
Yoshitatsu was born as the son of Masaki Yoshiyori and inherited the Masaki-Awaji-no-kami family. In 1578, after the Satomi and Gohōjō clans reconciled, he moved to Hyakushu Castle in Kazusa Province. In an Edo-period register dating from 1606 of clans, retainers, and their ranks and stipends, he received a stipend as a family member of 3,355 koku which was equivalent to the second-ranking highest member of the band of retainers of the Awa-Satomi.
Yoshitatsu’s eldest brother, Satomi Yoshiyasu, served as the first lord of the Tateyama domain in Awa Province. In 1590, he served in the Conquest of Odawara but invited the scorn of Toyotomi Hideyoshi for violations of the policy issued by Hideyoshi in the Kantō in 1587 prohibiting personal or territorial disputes between daimyō. As a result, Kazusa and Shimōsa provinces were seized and Yoshiyasu received official recognition of his rights only to Awa Province. At this time, owing to the intermediation of Tokugawa Ieyasu, the Satomi clan established friendly relations with the Tokugawa clan.
In 1600, after the Battle of Sekigahara, for his contributions, Yoshiyasu’s fief was increased by 30,000 koku in Kashima in Hitachi Province so the Tateyama domain attained daimyō status with a fief of 122,000 koku in total. Meanwhile, another older brother of Yoshitatsu, Satomi Tadashige, was assigned as the lord of the Itabana domain in Kōzuke with a fief of 10,000 koku. In 1603, Yoshiyasu died and was succeeded by his lineal heir, Satomi Tadayoshi. In 1613, Tadashige was suddenly removed from his position. In 1614, the Edo bakufu seized Awa Province from Tadayoshi in connection with the demotion of his father-in-law, Ōkubo Tadachika. In lieu of the landholdings in Kashima, he was transferred to Kurayoshi in Hōki Province. In fact, however, he was only granted enough rice for 100 people so the circumstances were akin to exile.
After the removal of the Satomi clan, Yoshitatsu wed the daughter of Naitō Ienaga (a retainer of the Tokugawa clan) and served the Naitō family.