Lifespan: Eishō 15 (1518) to Eiroku 5 (1562)
Other Names: Sena Yoshihiro → Sekiguchi Chikanaga
Title: Assistant Vice-Minister of Justice
Lord: Imagawa Yoshimoto → Imagawa Ujizane
Father: Sena Ujisada
Adoptive Father: Sekiguchi Ujiroku
Mother: Daughter of Horikoshi Sadamoto (?)
Siblings: Ujitoshi, Chikanaga, Ujitsugu
Wife: Younger sister of Imagawa Yoshimoto (adopted younger sister, daughter of Ii Naohira) (?)
Children: Masanaga, Michihide, daughter (wife of Ōtani Motohide), Tsukiyama-dono (formal wife of Tokugawa Ieyasu), daughter (wife of Hōjō Ujinori) (?)
Sekiguchi Chikanaga served as a bushō during the Sengoku period. Chikanaga was the head of the Imagawa-Gyōbu-shō family (or Imagawa-Sekiguchi family) and a powerful retainer of the Suruga-Imagawa clan. He served as the lord of Mochibune Castle in Suruga Province.
In 1518, Chikanaga was born as the second son of Sena Ujisada, a member of the Imagawa family.
He received one of the characters from the name of his lord, Imagawa Ujichika, and adopted the name of Chikanaga. In existing records, however, he signed his name as Ujizumi. He is deemed to have been wed to the younger sister of Imagawa Yoshimoto, but there is a theory that she was in fact married to his older brother, Sena Ujitoshi. Chikanaga was the father of Tsukiyama-dono, the formal wife of Tokugawa Ieyasu.
Chikanaga was adopted by Sekiguchi Ujiroku (the lord of Hanazawa Castle in Suruga) and inherited the headship of the Sekiguchi family. He served as a senior retainer of the Suruga-Imagawa and member of the hōkōshū, the military organ under the direct jurisdiction of the shōgun of the Muromachi bakufu.
Based on another theory, Sekiguchi Ujikane (Gyōbu-shō), who was the younger brother of Sekiguchi Masaoki (Gyōbu-taifu, a member of the hōkōshū), went to Suruga to serve the Imagawa clan and wed the daughter of Horikoshi Sadanobe (Imagawa Sadanobe) but died in 1525. His lineal heir, Gyōbu (Keiō) died soon thereafter so the son of Sena Ujisada, Sukegorō (Chikanaga, Ujizumi), became the adopted son-in-law and successor to the Sekiguchi clan. Masaoki’s son, 氏縁 (Hikosaburō, Gyōbu-taifu), served the Imagawa clan from around 1531, and his son, Sekiguchi Ujitsune (Echigo-no-kami) also served the Imagawa.
In the fifth month of 1560, at the Battle of Okehazama, Imagawa Yoshimoto was killed in a lightening attack by the Oda army. After this event, Chikanaga continued to serve the clan during their period of decline. After his son-in-law, Matsudaira Motoyasu (later known as Tokugawa Ieyasu), became independent of the Imagawa, Yoshimoto’s lineal heir, Imagawa Ujizane, suspected Chikanaga as having a role in the departure whereupon, in 1562, Chikanaga was ordered to commit seppuku at his residence in the town of Yakata in Sunpu.
Under one theory, Chikanaga planned to have Hōjō Ujinori (the nephew of Yoshimoto who was a hostage from the Gohōjō clan) become an adopted son-in-law and inherit the Sekiguchi clan (which was also the plan of Yoshimoto); however, after he was ordered to take his own life, the Gohōjō requested the return of Ujinori who then moved to Odawara Castle.