A Chōshū domain samurai and activist of the Bakumatsu anti-shogunate movement. Born into a middle-to-upper samurai family in Chōshū, he studied under Yoshida Shōin at the Shōka Sonjuku. His 1862 visit to Shanghai, where he witnessed the devastation wrought on China after the Opium War, steeled his resolve to overthrow the shogunate. In 1863, he founded the Kiheitai militia, which recruited talent regardless of social rank and revolutionized the traditional samurai-centered military system. At the Four-Border War (1866), he commanded Chōshū forces and led them to victory against the much larger shogunal army. Broken by tuberculosis from his relentless activism, he died in 1867 at the age of 27, on the eve of the Meiji Restoration. His death poem—"Making an interesting world out of a world that seems uninteresting: that is the work of the heart"—remains widely celebrated as an expression of the activist spirit.

A revolutionary of audacious boldness and genius creativity. He chafed at convention and social hierarchy, astonishing those around him with unconventional actions. Though short-lived, his blazing passion and outstanding leadership decisively shaped the course of the movement to overthrow the shogunate.

The founding of the Kiheitai anticipated the modern conscript army built after the Meiji Restoration. As a student of Yoshida Shōin, he carried forward the spirit of the Shōka Sonjuku and strongly influenced Meiji leaders such as Itō Hirobumi and Yamagata Aritomo. He remains celebrated as a hero of Yamaguchi Prefecture.