Lifespan: Unknown to 11/4 of Tenbun 21 (1552)
Clan: Mariyatsu-Takeda (Kazusa-Takeda clan)
Father: Mariyatsu Nobutaka
Children: Daughter (wife of Uesugi Yoshikatsu (known as Miyahara Yoshikatsu))
Mariyatsu Nobumasa served as a bushō during the Sengoku period. He was a member of the Mariyatsu-Takeda family based on the Bōsō Peninsula. Nobumasa served as the lord of Tsukuroumi and Shiizu castles in Kazusa Province.
Nobumasa was born as the son of Mariyatsu Nobutaka, a sengoku daimyō of Kazusa. Nobutaka was the eldest and illegitimate son of Mariyatsu Jokan (Nobumasa’s grandfather). After the death of Jokan, Nobutaka engaged in a succession struggle with his younger legitimate brother, Mariyatsu Nobumasa (written with a different character than the subject of this profile). This younger brother of Nobutaka was Nobumasa’s uncle. In the course of this conflict, Nobutaka joined with the Gohōjō clan of Sagami Province in revolt. At this time, Nobumasa was assigned to Tsukuroumi Castle to support his father at Minegami Castle.
Owing to intervention by Ashikaga Yoshiaki (the Oyumi kubō), Nobutaka found himself at a disadvantage so he abandoned Minegami Castle and fled to Tsukuroumi Castle. He was then attacked by Satomi Yoshitaka and, according to legend, he agreed to vacate the castle on the condition the Satomi forces deliver one hundred waka and spare the lives of the defenders. Thereafter, Tsukuroumi Castle was referred to as Hyakushu Castle, meaning the castle of one hundred poems. Relying upon the Gohōjō, Nobutaka fled to Musashi Province. Nobumasa is surmised to have accompanied his father during this period.
In 1538, at the First Battle of Kōnodai, Yoshiaki was killed in the course of a defeat to Hōjō Ujitsuna. Having lost his key patron, Nobumasa (Nobutaka’s brother) witnessed a weakening of his power, providing an opportunity for Nobutaka to reclaim his authority from his base at Shiizu Castle in Kazusa. Before long, internal conflicts reignited in the Mariyatsu family while the Gohōjō and Satomi clans intervened in Kazusa on the pretext of providing support. This led to a further decline in the influence of the Mariyatsu.
In 1551, Nobumasa’s father, Nobutaka, died. In 1552, Hōjō Ujiyasu of the Gohōjō clan plotted to ally with Nobumasa and the Toki clan of Mangi Castle to oppose the Satomi clan. Satomi Yoshitaka, however, rejected him and ordered Masaki Tokishige to attack Nobumasa. The Toki also acted in concert with the Satomi. Despite the support of his uncle (Nobutaka’s younger brother named Nobumasa), Nobumasa was defeated and took his own life at Shiizu Castle. Three days later, his uncle was also killed, marking a violent end to the Mariyatsu-Takeda family.