Kyojuro Rengoku held the position of Flame Hashira in the Demon Slayer Corps, continuing his family's legacy. His father, Shinjuro Rengoku, previously held the title but retired into alcoholism and apathy after the death of Kyojuro's mother, Ruka Rengoku, from illness. Ruka instilled in Kyojuro the principle that the strong must protect the weak, a creed central to his character. Despite his father's neglect and verbal abuse, Kyojuro maintained a close bond with his younger brother, Senjuro Rengoku, consistently encouraging him to pursue his dreams. Kyojuro achieved Hashira rank through self-directed study of the Flame Breathing style using only three volumes after his father ended his training. Kyojuro displayed an enthusiastic and optimistic personality, nearly always wearing a broad smile. He spoke loudly and energetically, commanding attention. He adhered strictly to the Demon Slayer Corps' rules and his personal morals, initially condemning Tanjiro Kamado for protecting his demon sister, Nezuko. Yet he demonstrated logical flexibility, accepting Nezuko after witnessing her defend humans on the Mugen Train. He possessed sharp tactical intelligence and swift decision-making, particularly under threat. He showed genuine interest in mentoring younger Demon Slayers, eagerly inviting Tanjiro, Zenitsu Agatsuma, and Inosuke Hashibira to become his apprentices (Tsuguko). He previously mentored Mitsuri Kanroji, who later became the Love Hashira, sharing a close, sibling-like bond with her. His final mission involved investigating disappearances aboard the Mugen Train, where he confronted Lower Rank One demon Enmu. After neutralizing earlier demon threats on the train and saving civilians, including a girl named Fuku and her grandmother, Kyojuro and the other Demon Slayers succumbed to Enmu's dream-inducing spell. Kyojuro’s spiritual core manifested as an inextinguishable flame, reflecting his unwavering resolve. Following Tanjiro’s awakening and Enmu’s defeat, Upper Rank Three demon Akaza attacked. Despite sustaining fatal injuries—a shattered eye socket, broken ribs, and a pierced solar plexus—Kyojuro fought Akaza relentlessly. He rejected Akaza’s offer to become a demon, declaring the nobility of human life lies in its fragility. In his final moments, he restrained Akaza to expose him to sunlight, forcing the demon to sever his own arms to escape. Kyojuro then assured Tanjiro his black Nichirin blade did not prevent mastery of a Breathing Style, urging him to consult Rengoku family records about Sun Breathing (Hinokami Kagura). He tasked Tanjiro with informing his father and brother of his condition and encouraged all present to persevere in protecting others. He died smiling, envisioning his mother. As Flame Hashira, Kyojuro wielded Flame Breathing techniques with exceptional mastery. His combat style combined immense physical strength, speed capable of causing ground tremors, and endurance that allowed him to fight through severe injuries like ruptured eardrums and gunshot wounds. His techniques included Unknowing Fire (a high-speed decapitating charge), Rising Scorching Sun (an ascending slash), Blooming Flame Undulation (a circular defensive motion), Flame Tiger (slashes forming a tiger-like shape), and his ultimate technique, Rengoku (a devastating dashing slash). Akaza, acknowledging Kyojuro’s proximity to the "Realm of the Highest," praised his fighting spirit and swordsmanship. Kyojuro also possessed extrasensory perception, detecting demonic presences faster than Tanjiro’s acute sense of smell and accurately assessing injuries or weaknesses. Kyojuro’s legacy endured through those he inspired. His final words—"Set your heart ablaze. Dry your eyes and look ahead"—and unwavering dedication profoundly impacted Tanjiro, Inosuke, and Zenitsu. The Hashira and the Demon Slayer Corps leader, Kagaya Ubuyashiki, honored him for preventing any passenger or comrade deaths during his final mission. His influence extended to his younger brother, Senjuro, whom he consistently supported despite their father’s disdain.