Along with lord of Morioka han Nanbu Toshihisa, lord of Hirosaki han Tsugaru Yukitsugu, and lord of Matsumae han Matsumae Takahiro, Yoshikuni was assigned by the shogunate in 1855 to take on guard duties in certain areas of Ezo.
Yoshikuni first married Konoe Tomoko (Tsuna-hime), a daughter of Takatsukasa Masahiro; following her death in 1852, in 1856 he then married Tokugawa Takako (Yashiro-hime), a younger sister of Tokugawa Yoshiatsu, lord of Mito han. Yoshikuni's adopted son Date Mochimura succeeded Tamura Kuniyuki to become lord of Ichinoseki han in 1857.
- Ishin Shiryô Kôyô 維新史料綱要, vol 2 (1937), 36.
- Ishin Shiryô Kôyô 維新史料綱要, vol 1 (1937), 342.
- Ishin Shiryô Kôyô 維新史料綱要, vol 2 (1937), 187.
- Ishin Shiryô Kôyô 維新史料綱要, vol 2 (1937), 356.