Born in the mountain village of Kawanoue in Tosa Domain, he grew up amid strict domain hierarchy and agrarian hardship. Early exposure to rangaku ideas and political unrest shaped his desire to reform Japan’s feudal order.

News of Commodore Matthew Perry’s black ships reached Tosa as he came of age, intensifying debates over defense and sovereignty. The crisis pushed him toward sonnō jōi activism and a belief that Japan needed stronger national leadership.

He pursued martial training while studying the politics of the late Tokugawa order, absorbing arguments for imperial restoration. In Tosa’s tense climate, young samurai debated reform, punishment, and loyalty with growing urgency.

He moved among activists influenced by figures like Takechi Hanpeita, where sonnō jōi rhetoric mixed with plans for direct action. These networks connected Tosa samurai to Kyoto’s volatile imperial politics and to other reform domains.

Kyoto’s streets were roiled by rōnin violence, shogunate police pressure, and shifting court alliances. He learned how negotiation, secrecy, and timing mattered as much as sword skill in Bakumatsu power struggles.

As the shogunate tightened surveillance after repeated incidents in Kyoto, he leaned further toward imperial loyalist collaboration. The widening crack between Tokugawa governance and reformist domains made him commit to national change.

In the aftermath of confrontations involving Chōshū and court politics, he deepened contacts with Chōshū leaders seeking allies. He came to see inter-domain cooperation as essential to resist Tokugawa reprisals and reshape government.

He developed a working partnership with Sakamoto Ryōma, another Tosa reformer pushing for maritime power and political unity. Their cooperation blended practical logistics with bold diplomacy, aiming to outmaneuver both domain barriers and shogunate controls.

Acting as a go-between, he supported efforts that aligned Saigō Takamori’s Satsuma with Kido Takayoshi’s Chōshū despite deep prior hostility. The alliance created a decisive anti-shogunate bloc and shifted the balance toward imperial restoration.

Using Nagasaki’s commercial channels, he helped arrange shipping, intelligence, and access to modern weapons for reformist forces. These maritime links reflected a new politics of trade and technology that contrasted with traditional domain isolation.

With Sakamoto Ryōma, he built the Kaientai as a hybrid of trading company, navy, and political organization rather than a standard clan unit. It trained men, moved supplies, and funded activism, modeling institutions for a modern nation-state.

He advocated replacing fragmented domain authority with a centralized political order tied to the imperial court. In meetings with allies and merchants, he argued modernization required coordinated finance, military reform, and broader participation beyond old ranks.

As Tokugawa Yoshinobu faced mounting pressure, he worked to keep reformist domains aligned and disciplined. He emphasized timing and coalition management, fearing internal splits could waste the moment for an orderly transfer of power.

While staying at the Omiya in Kyoto, assailants struck both him and Sakamoto Ryōma in a targeted attack linked to the era’s clandestine policing and rival factions. He was gravely wounded and left fighting for survival as politics raced ahead.

He succumbed to injuries in Kyoto only weeks before the final collapse of Tokugawa rule, never seeing the new government he helped midwife. His death, coming amid frantic negotiations and mobilizations, made him a martyr to restoration politics.

After his death, veterans and associates drew on Kaientai methods of logistics, training, and commerce as Japan centralized under the Meiji government. Memorialization in Tosa and Kyoto framed him as a decisive connector who turned ideals into alliances.