Assassination of Ōkubo Toshimichi (Kioichō Incident)

On the morning of May 14, 1878 (Meiji 11), Ōkubo Toshimichi, then Minister of the Interior and one of the most powerful figures in the Meiji government, was traveling by carriage from his residence in Kasumigaseki to the Akasaka Temporary Palace for an audience with Emperor Meiji. At around 8:30 a.m., as the carriage passed through Shimizudani in Kioichō, Kōjimachi-ku, Tokyo, it was attacked by six former samurai. The attackers first assaulted Ōkubo's servant, Yoshimatsu, who escaped and sought help nearby. They then killed the coachman, Nakamura Tarō, who had jumped from the carriage unarmed to confront them. Ōkubo was dragged from the carriage and killed, sustaining sixteen wounds according to a contemporaneous record. The assailants then discarded their swords, bowed to Ōkubo's body, and turned themselves in to authorities the same day, carrying a written manifesto known as the Zankanjō that listed grievances against senior government officials.

The six men involved — Shimada Ichirō, Nagare Tsuyoshi, Sugimoto Otsugiku, Wakita Kōichi, and Sugimura Bunichi, all from Ishikawa Prefecture, and Asai Toshiatsu from Shimane Prefecture — had backgrounds in earlier samurai-led unrest following the Meiji Restoration, including sympathy for the Seikanron debate and involvement in petitions and planning connected to the Satsuma Rebellion. After abandoning plans for an armed uprising, the group turned to a strategy of assassinating high officials. Riku Giyū drafted the Zankanjō at Shimada's request shortly before the attack.

Following the killing, roughly thirty people connected to the plot or its aftermath — including Riku, individuals asked to distribute the manifesto, and people who wrote letters expressing approval of the killing — were arrested in an extensive police investigation. The government classified the six assailants as "political offenders," a category not defined in existing criminal law, and created a Special Court under the Great Court of Cassation to try them. A draft judgment was prepared in July 1878, approved by the Council of State on July 25, and on July 27 the six men were sentenced and executed by beheading the same day. Riku Giyū was sentenced to life imprisonment and was later released in 1889 under a general amnesty.

In the aftermath, Ōkubo, who left significant personal debts due to his practice of funding public projects from his own funds, had his family's finances supported through government-arranged repayment and donations. Security escorts for senior government officials were increased following the incident, and the case is also cited in connection with the later administrative division of Ishikawa Prefecture, from which the assailants originated.