Hoshina Masayuki was a shogunal advisor and regent to the young Tokugawa Ietsuna, who succeeded his father Tokugawa Iemitsu at the age of ten. Hoshina was a son of Tokugawa Hidetada, half-brother to Tôfukumon-in, and uncle to the young shogun Ietsuna.
Though a son of a shogun, Masayuki was not born to Hidetada's primary wife, Tokugawa Eyo-no-kata, who forbade him, therefore, from staying within the household, and arranged to have him adopted by the Hoshina clan. He rose within the family to become daimyô of Aizu han, before returning to Edo to serve as shogunal regent for his young nephew.
In 1664, Hoshina helped resolve a domainal succession issue, when his son-in-law Uesugi Tsunakatsu, lord of Yonezawa han, died without a direct heir. Hoshina advised that the domain be split, and given to Uesugi Tsunanori. While this decision led to great financial difficulties for the domain, in the end, the Uesugi clan, continuing to feel indebted to Hoshina, and by extension to the Tokugawa clan, sided with the pro-shogunate Ôetsu Reppan Dômei in the Boshin War of 1868.
References
- Lillehoj, Elizabeth. "A Gift for the Retired Empress." in Lillehoj (ed.). Acquisition: Art and Ownership in Edo-Period Japan. Floating World Editions, 2007. p103.