The Banshū Disturbance (Banshū no sakuran) began in the eighth month of Meiō 5 (1496) and lasted until the end of Meiō 8 (1499). This disturbance was associated with a succession struggle that followed the death of Akamatsu Masanori, a sengoku daimyō and ninth head of the Akamatsu clan. It is alternatively referred to as Katsunori’s coup d’état. The term banshū is an alternative name for Harima Province.
Masanori did not have any sons, so, in 1489, he adopted Akamatsu Yoshimura, his son-in-law. On 4/25 of 1496, Masanori died suddenly, upon which Yoshimura became the head of the clan. However, owing to his sudden death, Yoshimura’s succession may not have been a result of the wishes of Masanori as much as those of senior retainers who wielded power in the Akamatsu clan at the time, including Uragami Norimune, Bessho Noriharu, Kodera Norimoto, Yakushiji Takayo, and Akamatsu Norisada.
While Yoshimura was young at the time of his succession, his wife, Komeshi, was eighteen when Yoshimura was adopted by Masanori, and Yoshimura is believed to have been a similar age. Accordingly, Yoshimura would likely have been an adult when he deployed to Nara three months after Masanori’s death. Masanori’s sudden death led to confusion within the clan, resulting in an internal conflict over the issue of succession. In this struggle, Uragami Norimune, a clan elder and a shugodai, or deputy military governor, supported Yoshimura, while Uragami Murakuni backed Akamatsu Katsunori. Finally, Bessho Noriharu supported Masanori’s widow (Tōshō-in) and adoptive mother of Yoshimura, to serve as an interim successor. Noriharu was concerned that if Yoshimura became the immediate successor, Norimune would take advantage of his youth to become further autocratic, so it was premature to grant full authority to Yoshimura. Therefore, he recommended that Tōshō-in serve as the interim head with the backing of Hosokawa Masamoto, the deputy shōgun, until Yoshimura matured.
In 1499, Uragami Murakuni joined with Akamatsu Katsunori against Uragami Norimune in a revolt known as the East-West Battle of Harima (Tōzai-toriai kassen). Norimune narrowly escaped owing to a valiant defense by Ukita Yoshiie, taking Yoshimura to Shioya Castle held by Uno Masahide. While providing sanctuary to Norimune, Masahide backed Yoshimura as the successor. Masahide then directed Tōji Sakyō-no-suke to attack Murakuni, while Masahide himself went to Kyōto to request mediation by Hosokawa Masamoto, and an Imperial edict for a cessation of hostilities from Ashikaga Yoshizumi, the eleventh shōgun. The family members eventually reconciled, with Yoshimura becoming the successor. In 1502, Norimune died in Mitsuishi Castle in Bizen Province, while Tōshōin continued to serve an influential role in the clan alongside Yoshimura.