Lifespan: Unknown to 2/4 of Eiroku 5 (1562)
Title: Governor of Nagato
Lord: Imagawa Yoshimoto → Imagawa Ujizane
Father: Udono Nagamochi
Mother: Daughter of Imagawa Ujichika
Siblings: Nagateru, Nagatada, Matsudaira Kiyoyoshi (?), Nishinokōri-no-tsubone (?) (she may have been an adopted daughter; later a consort of Tokugawa Ieyasu), sister (wife of Matsudaira Koretada), Otazu-no-kata
Children: Ujinaga, Ujitsugu
Udono Nagateru served as a bushō during the Sengoku period. Nagateru served as a retainer of the Imagawa clan and as the lord of Kaminogō Castle in the Hoi District of Mikawa Province.
In 1557, following the death of his father, Udono Nagamochi, Nagateru inherited the headship of the clan. (According to one other military chronicle of Mikawa, Nagamochi died in 1562). In the context of the policy of the Imagawa clan to expand west, the implication of the territory held by the Udono clan connecting Mikawa from east to west became very important to this plan. By forming a connection, the status of the Udono increased among the Imagawa who aimed to secure the western route. Nagateru’s natural mother was the younger sister of his lord, Imagawa Yoshimoto, as a nephew, Nagateru was relied upon by the Imagawa family.
Prior to the Battle of Okehazama in 1560, Nagateru was appointed as the chamberlain of Ōdaka Castle. The castle, however, was situated on the front lines with the Oda, so his ability to move was constrained while he confronted a scarcity of provisions. In an effort to raise the spirits of his garrison, Nagateru picked fruit from trees in the surrounding hills and fields to overcome the hunger. Nagateru was praised for supplying provisions upon the direction of Matsudaira Motoyasu (later known as Tokugawa Ieyasu) during a preliminary skirmish to the Battle of Okehazama. Having escaped from a precarious situation, Nagateru was replaced by Motoyasu in Ōdaka Castle. His next assignment and movements thereafter are uncertain. After the Battle of Okehazama in which Imagawa Yoshimoto was killed by Oda forces led by Oda Nobunaga while stopping to rest during a march through Owari, Nagateru fled to Mikawa in advance of Motoyasu.
After Imagawa Ujizane became head of the clan in the wake of his father’s death at the Battle of Okehazama, the territory under the governance of the Imagawa descended into political chaos. In particular, the influence of the Imagawa waned in Mikawa, enabling Matsudaira Motoyasu to gain prominence. Many former retainers of the Imagawa in the territory switched their allegiance to the Matsudaira but, owing to their familial ties, the Udono remained loyal to the Imagawa. Nevertheless, this was limited to the main branch of the Udono based at Kaminogō Castle who maintained close relations with the Imagawa clan as their relatives, while cadet families of the Udono based at Shimonogō Castle (Kamagata Castle) aligned with the Matsudaira. Motoyasu then entered into a military alliance with Oda Nobunaga, an event known as the Kiyosu Alliance, further adding to the autonomy and separation of the Matsudaira from the Imagawa. This led to an increasingly hostile relationship between the Matsudaira and the main branch of the Udono who continued to support the Imagawa in Mikawa.
In 1562, Matsudaira forces attacked the Udono at Kaminogō Castle, and although the defenders initially repelled the assaults by the vanguard forces including Matsudaira Kiyomune, the castle eventually fell. Nagateru, along with his father, Nagamochi, died in action. During the fall of the castle, Nagateru’s sons, Udono Ujinaga and Udono Ujitsugu, were apprehended. Motoyasu then made a deal with Imagawa Ujizane to exchange the brothers for the return of Motoyasu’s formal wife (Senahime or Tsukiyama-dono), eldest son (Takechiyo or Matsudaira Nobuyasu) and eldest daughter (Kamehime) whom he had earlier tendered as hostages to Imagawa Yoshimoto during his period of service to the clan.
According to one theory, during the fall of Kaminogō Castle, Nagateru narrowly escaped from the castle but was later killed by Ban Sukesada on a hill alongside the Anraku Temple. This site was named Udono Hill and, owing to the misfortune experienced by Nagateru, there is a legend that if you fall on this hill, your injuries will not heal for the rest of your life.