Lifespan: Tenbun 5 (1536) to Eiroku 11 (1569)
Clan: Kira (a branch of the Seiwa-Genji Ashikaga family)
Lord: Tokugawa Ieyasu
Father: Kira Yoshitaka
Adoptive Father: Kira Mochihiro
Siblings: Yoshisato, Yoshiyasu, Yoshiaki
Wife: [Formal] Shunkeini (daughter of Matsudaira Kiyoyasu)
Children: Yoshisada, daughter (wife of Imagawa Norimochi, second wife of Ōinomikado Tsuneyori)
Kira Yoshiyasu served as a bushō in Mikawa Province during the Sengoku period.
The Mikawa-Kira clan was divided into the Tōjō-Kira and the Saijō-Kira on either side of the Yahagi River. Yoshiyasu originated from the Saijō-Kira based at Nishio Castle in Nishio, but was adopted to serve as the head of the Tōjō-Kira clan. Later, he served Tokugawa Ieyasu and also became the head of the Saijō-Kira clan. His common name was Saburō.
In 1536, Yoshiyasu was born as the second son of Kira Yoshitaka, the lord of Saijō Castle. His mother may have been Yoshitaka’s formal wife (the daughter of Imagawa Ujichika and older sister of Imagawa Yoshimoto) or the daughter of Gotō Heidayū, a member of the Gotō clan in the hōkōshū, the military organ of the Muromachi bakufu under the direct control of the Ashikaga shōgun. Initially, Yoshiyasu’s older brother, Kira Yoshisato, succeeded to the headship of the Saijō-Kira clan while Yoshiyasu was adopted by Kira Mochihiro, the head of the Tōjō clan and lord of Tōjō Castle. Yoshisato, however, died early (under one theory, in battle against Imagawa Yoshimoto of Suruga), so Yoshiyasu returned to the Saijō-Kira clan to succeed Yoshisato. Mochihiro then died, so Yoshiyasu’s younger brother, Kira Yoshiaki, inherited the Saijō-Kira while Yoshiyasu inherited the headship of the Tōjō-Kira. However, Yoshiyasu did not consent to this succession plan, and entered Nishio Castle as the head of both branches of the Kira family. He then came into conflict with retainers of the Saijō-Kira who opposed him so he joined with the Shiba and Oda clans to oppose them.
In 1549, when Imagawa Yoshimoto, a sengoku daimyō from Suruga Province, attacked Oda Nobuhiro, the lord of Anjō Castle and a retainer of the Oda clan, Yoshiyasu cooperated with the Oda clan, so he was apprehended by the Imagawa army and taken as a hostage to their base in Sunpu. At this time, however, Yoshiyasu’s younger brother, Kira Yoshiaki, cooperated with the Imagawa army, so he was ordered to take over the Tōjō-Kira clan. As a result, Yoshiaki unified the Saijō-Kira and the Tōjō-Kira branches and submitted to the governance of the Imagawa family. Gotō Heidayū, surmised to have been Yoshiyasu’s grandfather, was executed for his role as the ringleader of the opposition to the Imagawa.
For over the next ten years, Yoshiyasu lived as a hostage in Sunpu during which time he became friendly with Matsudaira Takechiyo (later known as Tokugawa Ieyasu) who had similarly served as a hostage of the Imagawa clan. In 1555, when Ieyasu underwent his coming-of-age ceremony, Yoshiyasu assisted with his hair styling. In the sixth month of 1560, Imagawa Yoshimoto was killed in an attack by Oda Nobunaga at the Battle of Okehazama, so, along with Ieyasu, he was released from his status as a hostage and returned to Mikawa.
According to one account, Imagawa Ujizane suspected Yoshiyasu of rebelling, so he detained Yoshiyasu in Suruga and, instead, moved Yoshiaki to Tōjō and had him unify the two branches of the Kira. Under another account, with respect to rebellions by the Kira during the Kōji era (1555 to 1558), after Yoshiyasu spent time in Sunpu as a hostage, at one time he was pardoned and allowed to return to Mikawa as the head of the unified Kira family. In 1555, however, after rebellion against the Imagawa for a second time, in 1557, he was ultimately ousted from Mikawa. Moreover, based on a large-scale survey conducted in 1557 by the Imagawa of the Saijō-Kira territory, Nishio Castle and this area came under the direct control of the Imagawa despite Yoshiaki’s ostensible role as the head of the unified Kira family.
Early in the fourth month of 1557, at a conference held in Uenohara in Mikawa, Shiba Yoshimune (the military governor of Owari backed by Oda Nobunaga) aimed to form an alliance with the Kira clan (military governors of Mikawa) and Imagawa clan (sengoku daimyō of Suruga) as members of the Ashikaga clan. This meeting was attended by Nobunaga on behalf of the Shiba and Yoshimoto on behalf of the Kira. At this time, the two likely saw each other for the first time. At the meeting place, Kira Yoshiyasu and Shiba Yoshimune each sat on folding stools in front of their respective contingents. Given their respective status as high-ranking members of the Ashikaga family, a dispute arose in regard to the seating order, and neither side compromised, so the meeting was limited to each side advancing ten steps forward to face one another and, without any formal greetings, the conference ended.
Under one theory, after the failed reconciliation, Yoshiyasu could not remain in Mikawa and fled to Owari. Meanwhile, after plotting with the Ishibashi clan to expel Nobunaga, Shiba Yoshimune was ousted from Owari and, after returning to Mikawa, was incarcerated against by Imagawa Ujizane. After the rebellion in 1549, the main branch of the Imagawa clan gave careful consideration to the position of the Kira clan, pardoned Yoshiyasu, and guaranteed his status as the head of both branches of the Mikawa-Kira clan, only to be betrayed again, so thereafter gave their support to Yoshiaki.
Meanwhile, after losing the backing of the Imagawa, Yoshiyasu’s younger brother, Yoshiaki, became isolated and was compelled to submit to Tokugawa Ieyasu. In 1562, Yoshiaki sought to revive his clan by joining forces with followers of the Mikawa Ikkō sect to fight against the Tokugawa clan, an event known as the Mikawa Ikkō-ikki, but lost and fled Mikawa. Thereafter, Ieyasu recognized Yoshiyasu’s control of the unified branches of the Kira clan and associated territorial rights.
Under Yoshiyasu, the unified Mikawa-Kira clan served the Tokugawa family which continued until the removal of Kira Yoshihisa owing to his involvement in a killing known as the Akō Incident.