Lifespan: Genki 1 (1570) to 10/24 of Tenshō 10 (1582)
Rank: sengoku daimyō
Father: Nanbu Harumasa
Siblings: Sister (formal wife of Nanbu Nobunao), sister (formal wife of Kunohe Sanechika), sister (formal wife of Kita Hidechika), Harutsugu
Nanbu Harutsugu served as a sengoku daimyō of Mutsu Province during the Azuchi-Momoyama period. He was the twenty-fifth head of the Nanbu clan.
In 1570, Harutsugu was born as the son and designated heir of Nanbu Harumasa, the twenty-fourth head of the Nanbu clan. After having several daughters, prior to the birth of Harutsugu, Harumasa had given-up on having a natural son, so he arranged for his eldest daughter to wed Takko Nobunao (later known as Nanbu Nobunao) who was the eldest son of Harumasa’s uncle, Ishikawa Takanobu. Nobunao then became Harumasa’s adopted son-in-law and designated heir based at Sannohe Castle. After the birth of Harutsugu, however, Harumasa gradually became estranged from Nobunao and, in 1576, Harumasa removed Nobunao from the line of succession while Harutsugu became his designated successor.
In 1577, at the time of Harutsugu’s coming-of-age ceremony, a retainer named Kita Nobuchika served in an honorary role to place the black-lacquered headgear known as an eboshi upon Harutsugu. There are several theories concerning the year of his succession, including 1573, 1577, or 1582. Nevertheless, the adoptive relationship between Harumasa and Nobunao was retracted in 1576. This limits the likely theories to 1577 or 1582. Given his youth, however, it is surmised that he inherited the headship of the clan upon the death from illness of Harumasa in the first month of 1582.
Less than three weeks later, Harutsugu was attacked and slayed while returning at night to Sannohe Castle after the funeral for his father. In this case, the killing may have been directed by either Nobunao or a powerful figure in the Nanbu clan named Kunohe Masazane who opposed the succession by Harutsugu. Under another theory, Harutsugu died of smallpox, but, owing to the timing of his death so soon after his father, and in the midst of an intense succession struggle, the intentional killing is a more compelling theory. Finally, there is a theory that Harutsugu and his father were killed together in a rebellion by Nobunao. In any event, the death of Harutsugu so soon after his father resulted in an ephemeral role for him as a sengoku daimyō, triggering a succession struggle in which Nobunao prevailed with backing from Kita Nobuchika. Thereafter, Nobuchika became a close associate of Nobunao, managing internal affairs as well as external diplomacy for the Nanbu clan.