Kikuchiyo is a central character who serves as the seventh member of the titular group of warriors. His background is marked by humble and difficult origins. He was originally a farmer in a remote village, a past that shaped much of his worldview and his deep-seated resentment toward both the bandits who terrorize the countryside and the samurai class that often oppresses the common people. Unable to continue living as a peasant, he decided to become a samurai and, to gain the physical power necessary for this new path, he underwent a process to mechanize his body with a steam-powered exoskeleton. The name "Kikuchiyo" is not his original name; it was taken from a family tree he acquired or stole, which ironically identified him as a thirteen-year-old girl, a fact that later becomes a source of humiliation.

In terms of personality, Kikuchiyo is a boisterous, loud, and often clumsy individual. Due to his short temper and the trouble he frequently causes with his noisy and brash demeanor, he is initially looked upon by others as a clown or a bother rather than a proper samurai. Beneath this rough and seemingly foolish exterior, however, lies a devoted, passionate, and deeply likeable person. He possesses a strong sense of empathy, particularly for the weak, including farmers and children, and he openly shows kindness to those who are vulnerable. Despite his bravado and constant claims of being a great warrior, he carries a significant amount of insecurity due to his artificial body and peasant origins, and he desperately seeks recognition and a place to belong.

His primary motivation is to be accepted as a true samurai and to find a sense of purpose. This drive leads him to join the mission to defend the village of Kanna from the Nobuseri bandits. Throughout the story, his role evolves from that of an unwanted, eccentric hanger-on to a crucial and irreplaceable member of the team. Initially not counted as a real fighter by the leader Kambei, Kikuchiyo's moment of true acceptance comes when a villager's betrayal reveals that farmers can be cowardly and deceitful. In a powerful, emotional outburst, Kikuchiyo reveals his own past as a farmer, delivering a scathing speech about how the samurai class itself is responsible for creating such desperate and untrustworthy peasants. This raw display of understanding and honesty finally convinces Kambei to acknowledge him as the seventh samurai.

Kikuchiyo's key relationships are central to his development. His loyalty to the veteran samurai Kambei is fierce, and he seeks the man's approval above all else. He also forms a close friendship with the easygoing samurai Heihachi, who treats him with respect. His connection to the villagers, however, is where his softer side shines brightest. He becomes particularly close to a young girl named Komachi, the sister of the village's shrine maiden, who calls him "Mr. Samurai" and asks him to marry her when she grows up. Kikuchiyo accepts this request, asking her to keep his fake family tree safe in return, showing a tender and heartfelt bond.

Throughout the narrative, Kikuchiyo undergoes significant development. He starts as a tragic, sad clown figure, overcompensating for his lack of pedigree with noise and bluster. As the story progresses, he proves his worth not just with his strength, but with his strategic resourcefulness and his role as the emotional conscience of the group. He is often the one who reminds the other samurai of what they are truly fighting for and connects with the farmers on a level they cannot. This journey culminates in his final act of heroism. He is the last of the samurai to fall, dying to protect the village of Kanna from a massive, crashing section of the capital city. In his final moments, he overexerts his mechanical body to stop the falling object, refusing to retreat until his body is almost entirely destroyed, leaving only his two feet planted in the ground, showing he never took a single step back.

Kikuchiyo's notable abilities are directly tied to his cyborg nature. His mechanized exoskeleton endows him with immense superhuman strength and incredible resilience, allowing him to survive injuries that would be fatal to a normal human, such as dismemberment or decapitation. He wields a proportionally gigantic sword that is reinforced to resonate at high frequencies, effectively turning it into a powerful chainsaw capable of cutting through almost anything. While his fighting style is less refined and lacks the elegant technique of his comrades, his raw, brute force more than compensates, making him a devastating force on the battlefield.