In February 1859, the daimyō of Tosa Domain Yamauchi Yōdō, was forced from office and placed under house arrest by the tairō Ii Naosuke for his efforts to establish Hitotsubashi Yoshinobu as successor to the shogunate.
The Sonnō jōi movement also spread quickly in Tosa, after many were alarmed by the arrival of the Perry Expedition in 1858 and what they perceived to be the weak response of the Tokugawa shogunate to this threat.
In May 1860, Takechi went on a tour of Kyushu and western Japan with a number of his closest disciples, and returned with some of the works of kokugaku scholar Hirata Atsutane, which further reinforced his belief in the Sonnō jōi movement.
In April 1861, Takechi returned to Edo under the guise of practicing swordsmanship, but in reality to meet with like-minded samurai of various domains, including Katsura Kogōrō, Kusaka Genzui, and Takasugi Shinsaku of Chōshū, Kabayama Sanin from Satsuma and Iwama Kanpei from Mito.
Although Tōyō originally had a weak political foundation, the former feudal lord Yamauchi Yōdō, who had been his backing, had fallen from power due to the Ansei Purge, and he was dissatisfied with his policy of reforming the domain system.
Eventually, Takechi decided that his only course of action would be to assassinate Yoshida and to kidnap the young daimyō, Yamauchi Tomonori en route to Edo on his sankin kōtai.
In September the following year, an uprising of samurai sympathetic to Takechi was suppressed and the roundup of Tosa Kinnō-tō members and supporters continued.