Ogasawara Nobuoki served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was the lord of Takatenjin Castle in the Kitō District of Tōtōmi Province.  Nobuoki appears in military chronicles under the name of Nagatada, but his childhood name was Ujisuke and later changed to Nobuoki.  In the authenticated biography of Oda Nobunaga known as the Shinchō-kōki, Nagatada and Nobuoki (Ujisuke) are treated as separate individuals, leading to inconsistencies in later historical texts and research.

Origins

Nobuoki originated from the Takatenjin-Ogasawara clan of Tōtōmi Province, an illegitimate branch of the Ogasawara clan of Shinano Province.  In the era of Nobuoki’s grandfather, Ogasawara Haruyoshi, the Takatenjin-Ogasawara the Fukushima clan serving as the lords of Takatenjin Castle at the time fell into ruin as a result of a succession struggle in the Imagawa clan of Suruga Province known as the Hanakura Conflict occurring in 1536.  As retainers of the Imagawa, the Takatenjin-Ogasawara gained prominence in lieu of the Fukushima.  The character “haru” in the name of Haruyoshi was customarily used by the Fukushima clan but, thereafter, those serving as lords of the castle were conferred the character “uji” from the Imagawa clan and treated on a par with members of the family.

The character “uji” in his childhood name of Ujisuke was conferred from his father while the character “suke” was customarily used by the Ogasawara clan.  Nobuoki inherited the headship of the clan after his father, Ogasawara Ujioki, entered the priesthood by the first month of 1568 and retired at Mamushizuka Castle.

Service as a retainer of the Tokugawa clan

Nobuoki served Imagawa Yoshimoto and his son, Imagawa Ujizane but, in 1568, the Invasion of Suruga by Takeda Shingen of Kai Province led to the fall of the Imagawa clan.  Thereafter, Nobuoki affiliated with Tokugawa Ieyasu of Mikawa Province who seized control of Tōtōmi Province from the Imagawa.  Upon serving Ieyasu, he was assigned to the front lines opposing the Takeda clan.   In 1570, Nobuoki contributed on behalf of the Tokugawa at the Battle of Kanegasaki in Echizen Province and, several months later, at the Battle of Anegawa in Ōmi Province.

In 1572, Takeda Shingen commenced an invasion of the territory of the Tokugawa.  On 10/21, Nobuoki surrendered in the wake of an attack by the main division of the Takeda army under Shingen.  After the withdrawal of the Takeda army, Nobuoki appears to have reverted to the Tokugawa clan.

In the sixth month of 1574, Takeda Katsuyori led a formidable army of 25,000 soldiers to assault Takatenjin Castle.  This is known as the First Siege of Takatenjin Castle.  Nobuoki urgently requested reinforcements from Ieyasu, but Ieyasu could not grant his request.  Ieyasu, in turn, made a request to Nobunaga but it was to no avail.  During a siege that ran for approximately sixty days, the Takeda forces breached several baileys while Honma Ujikiyo, Maruo Yoshikiyo, and Takanashi Hidemasa were all killed in the course of the battles.  Only the main bailey surrounding the keep remained in the hands of the defenders.  As a result, Nobuoki agreed to vacate the castle in exchange for having spared the lives of his soldiers.

Ujisuke (Nobuoki) was conferred a name by Katsuyori and, thereafter, was called Danjō-Shōhitsu Nobuoki.

Service as a retainer of the Takeda clan

Even after surrendering to the Takeda clan, Nobuoki received recognition of his rights to Takatenjin Castle along with the security of the temples and shrines in the territory.  In the fifth month of 1574, the Takeda army suffered an overwhelming defeat to the allied army of the Oda and Tokugawa at the Battle of Nagashino.    to To prepare for a counterattack by the Tokugawa army, Nobuoki reinforced the defenses at Takatenjin Castle and between the tenth month of 1574 and the eleventh month of 1575, he was transferred to Omosu in the Fuji District of Suruga with a fief of 10,000 kan.

After leaving Takatenjin Castle, Nobuoki was active in the eastern portion of Suruga.  In the ninth month of 1578, Katsuyori attempted to transport provisions to Takatenjin Castle but this was interdicted by Ieyasu and Matsudaira Nobuyasu who advanced to Mamushizuka Castle.  Meanwhile, the Takeda attacked Yokosuka Castle defended by Ōsuga Yasutaka during which Nobuoki served in the vanguard of the Takeda forces.  After disputes broke-out between the Taked and Gohōjō clans, Nobuoki served under Sone Kawachi-no-kami of Sanmaibashi Castle in Suruga in battle against the Gohōjō.  In the eighth month of 1581, he returned to the village of Sudo in the Fuji District of Tōtōmi.

Following the decimation of the Takeda clan in the third month of 1582, Nobuoki’s whereabouts are unknown.  According to records of the Hōjō clan, Nobuoki relied upon Hōjō Ujimasa and fled to Odawara but was then murdered by Ujimasa upon orders of Oda Nobunaga.  Based on other materials, Nobuoki was protected by Ujimasa but in 1590, after the fall of the Hōjō clan, he was apprehended by Ieyasu, censured for his previous surrender to the Takeda, and executed.  Yet, under another theory, during a tense period between Hashiba Hideyoshi and Tokugawa Ieyasu manifested in the Battle of Komaki-Nagakute, the Tokugawa clan entered into an alliance with the Hōjō clan bound via marital relationships.  Around this time, upon the wishes of Ieyasu after he learned that Nobuoki had been harbored by the Hōjō clan and retired in Kamakura, he was punished at the hands of the Hōjō.  In any event, there are no primary sources of information to validate the facts surrounding the end of his life.

Thereafter, his uncle, Ogasawara Yoshiyori, is deemed to have inherited the headship of the Takatenjin-Ogasawara.