Masuda Nagayuki served as a bushō during the Sengoku period. He was a chief retainer of the Awa-Tokushima domain. Nagayuki came from Owari Province and served as the lord of Awa-Ichinomiya Castle and Kaifu Castle.
Nagayuki was born as the eldest son of Masuda Kazumasa, a retainer of the Hachisuka family. Kazumasa served as the lord of Awa-Ichinomiya Castle and Kaifu Castle, and Nagayuki inherited these roles from his father.
While serving as the chamberlain of Kaifu, he was awarded a fief of 5,500 koku and served in the Battle of Sekigahara and the Siege of Ōsaka. In 1619, he served with those accepting the turn-over of Hiroshima Castle.
In accordance with a policy of the Edo bakufu known as sankin-kōtai by which daimyo alternated between their home province and a residence in Edo, Nagayuki frequently traveled to Edo, during which he established friendly relations with a chief minister named Sakai Tadayo. By leveraging his connections in the bakufu, Nagayuki plotted to achieve independence as the lord of the Kaifu District in Awa. In furtherance of this plan, he violated a prohibition by harvesting trees and transporting them to Edo to generate funds. Nagayuki was then subject to prosecution by officials of the Tokushima domain, resulting in the confiscation of his landholdings and his incarceration for the next thirteen years. Resentful of this treatment, by 1645, Nagayuki claimed that Hachisuka Tadateru, the lord of the Tokushima domain, violated a prohibition of the bakufu by constructing a large vessel and, further, was negligent in carrying out the religious census used to repress Christians as dictated by the bakufu.
In 1646, the bakufu conducted a hearing between Nagayuki and Hasegawa Sadatsune, a chief retainer of the Tokushima domain. Nagayuki’s claims were found to be falsehoods and he was transferred to the custody of Tadateru. This series of events is known as the Kaifu Disturbance.
In 1646, while traveling from Edo to Awa, Nagayuki died of illness. According to another theory, he was slayed at his residence in Edo.
His grave is at the Jōroku Temple in the town of Jōroku in the city of Tokushima in Tokushima Prefecture.