The roots of the Kennin Rebellion reach back to the Genpei War of 1180 to 1185, when the Taira and Minamoto clans tore Japan apart in their struggle for supremacy. The Jo clan, descended from a Taira branch and based in Echigo Province, fought on the losing side. When Minamoto no Yoritomo emerged victorious and established the Kamakura shogunate, he pardoned the Jo clan rather than destroying them. Their leader, Jo Nagamochi, played the long game. He assisted the Minamoto in campaigns against the Northern Fujiwara, gradually earning the trust of the new government. His survival owed much to the patronage of Kajiwara Kagetoki, an influential figure in the shogunate. But the Jo clan's power had been shattered, and Nagamochi's resentment smoldered. He spent years planning to overthrow the regime that had humiliated his family.

Jo Nagamochi launched his rebellion on New Year's Day, January 1201, striking at the capital of Heian-kyo. The revolt collapsed almost immediately. Nagamochi tried to flee to Mount Yoshino but was captured and beheaded. With the clan's leader dead, the shogunate turned its attention to the Jo family's remaining forces in Echigo Province, where Jo Sukemori had rallied what was left of the rebel army at Tossaka Castle. Sukemori agreed to a final stand. The main battle came in May, with his troops fighting outside the walls while the defense of the castle itself fell to Hangaku Gozen, Sukemori's relative and a warrior already renowned among her followers for her extraordinary skill with a bow.

Dressed in full samurai armor, Hangaku Gozen commanded the castle garrison from a tower, raining arrows down on the attacking force with devastating accuracy. She was an inspirational leader, her presence on the walls stiffening the resolve of the defenders even as their situation grew desperate. The siege might have continued longer had a samurai named Fujisawa Kiyochika not climbed a nearby mountain, found a blind spot at the castle's rear, and put an arrow through a gap in her armor. The shaft struck her thigh, piercing her legs at an unprotected point. Unable to stand, she collapsed. With her fall, the garrison surrendered on May 9th. Jo Sukemori fled the field and reportedly managed to hide in Dewa Province, though his ultimate fate remains uncertain.

In June 1201, Hangaku Gozen was sent to Kamakura and presented to Minamoto no Yoriie, the shogun. What should have been a moment of utter humiliation became something else entirely. Observers noted her fearlessness, her proud stance as she faced the man who held her life in his hands. Captured alive and paraded before the court as a curiosity, she showed no submission. By the conventions of the era, she should have been ordered to commit seppuku or sentenced to lifelong exile. Instead, a samurai in Yoriie's retinue named Asari Yoichi Yoshito stepped forward, captivated by her demeanor, and asked to marry her. When the shogun demanded an explanation, Asari reasoned that such a warrior would surely bear a strong son who would defend the shogun. Yoriie laughed and mocked Asari, claiming Hangaku Gozen was so unwomanly she had no attraction to men. But Asari persisted, and the shogun relented.

Asari and Hangaku Gozen married and had at least one child. Whether it was a son or a daughter depends on which historical account one follows; the historian Bun'ei Tsunoda states it was a girl. The rebellion itself faded into relative obscurity, overshadowed by the larger dramas of the Kamakura period. It took its name from the Kennin era during which most of the fighting occurred. But Hangaku Gozen's story refused to die. Over the centuries, legends about her feats and strength multiplied. Utagawa Kuniyoshi depicted her in full armor around 1842, bow drawn, embodying the onna-musha tradition of female warriors that challenged the image of women in feudal Japan. Today, the city of Tainai honors her with a statue at Nakajo Station, a permanent reminder that the rebellion's most enduring figure was not the man who started it, but the woman who nearly saved it.