Lifespan: 15xx to 11/29 of Eiroku 5 (1562)
Title: Governor of Kii
Lord: Imagawa Yoshimoto → Imagawa Ujizane
Father: Asahina Tokishige
Siblings: Chikataka, Yasunaga, Mototomo
Children: Yasumitsu, Matsugi
Asahina Yasunaga served as a retainer of the Imagawa and lord of Utsuyama Castle in Tōtōmi Province. Yasunaga was the second son of Asahina Tokishige, who held the Court title of Provincial Governor of Shimotsuke. Asahina Yasuyoshi, a senior retainer of Imagawa Yoshimoto, was a younger cousin of Yasunaga.
Owing to the location of Utsuyama Castle on the western shore of Lake Hamana, Yasunaga was responsible for protecting the border area between Tōtōmi and Mikawa provinces, and, in particular, the Yana District in the eastern portion of Mikawa. In 1561, Matsudaira Motoyasu became independent of the Imagawa and changed his name to Tokugawa Ieyasu. Yasunaga quickly mobilized forces after the kokujin in eastern Mikawa planned an uprising. The forces crossed the provincial border into Mikawa and launched a sudden attack against Gohonmatsu Castle, the home base of the Saigō clan in the Yana District of Mikawa. Saigō Masakatsu, lord of Gohonmatsu, attempted to defend the castle. His eldest son, Saigō Motomasu, came from his base at Wachigaya Castle to offer support, but to no avail against a superior number of attackers. Both perished. Early in 1562, Masakatsu’s second son, Saigō Kiyokazu, led forces of the Tokugawa army to Katsuyama in the Yana District on the shore of the Toyo River, and clashed with the invaders in Kamo. He lost this battle and fled to territory held by the Saigō.
Yasunaga died later in 1562 and was memorialized on Mount Utsu. In 1563, his eldest son, Yasumitsu, was slayed by his second son, Matsugi, whereupon Matsugi became lord of Utsuyama Castle and held the Court title of Provincial Governor of Kii. Matsugi was wed to the eldest daughter of Honda Tadatoshi, lord of Nara Castle in the Hoi District of Mikawa, who had pledged allegiance to the Tokugawa clan. Through this connection, Matsugi may have colluded with Tokugawa Ieyasu. Consequently, Yasunaga’s descendants served as retainers to the Tokugawa bakufu in the Edo period.