Hyakkimaru is the central figure of a dark historical fantasy narrative set in Japan's Sengoku period. He is a young ronin, or masterless samurai, whose very existence is the result of a tragic and monstrous pact. Before his birth, his biological father, the ambitious lord Daigo Kagemitsu, made a deal with a group of demons to gain power over his war-torn lands. In exchange for this prosperity, the demons claimed the body of Kagemitsu's unborn son. Consequently, Hyakkimaru was born into the world as a malformed infant, missing forty-eight parts of his body including his limbs, facial features, and internal organs. Viewing the child as a curse, his father ordered him to be cast away, but the infant was saved when he was found floating down a river by a skilled prosthetics maker named Dr. Jukai.

Jukai raised Hyakkimaru as his own son, crafting a set of prosthetic limbs that allowed him to move and fight. The most critical of these prosthetics are blades hidden within his forearms, which he uses as his primary weapons. Due to his profound physical disabilities, Hyakkimaru developed a powerful sixth sense, an extrasensory perception that allows him to see the world not through sight, but by perceiving the souls or spiritual auras of living beings and demons. This ability gives him an excellent judge of character, as he can discern a person’s true nature by the color of their soul, unclouded by outward appearances. However, it also means he experiences the world in a deeply abstract way, without the context of normal human senses like sight, sound, or touch.

In terms of personality, Hyakkimaru begins his journey as a stoic, almost feral individual, completely defined by his singular purpose. Having been deprived of most physical sensations and social interaction, he initially displays a complete lack of emotion, no social skills, and no understanding of concepts like fear or pain. His existence is a relentless, almost mechanical pursuit of the demons who possess his body parts. He fights as a berserker, launching attack after attack without any regard for his own safety, a trait born not from courage but from the simple fact that he cannot feel the injuries he sustains. This single-mindedness makes him seem cold and detached, focused only on his goal of becoming whole.

Hyakkimaru's primary motivation is the physical and spiritual reclamation of his own body. Each time he slays one of the twelve demons that holds his flesh, a body part is returned to him. This process is not a simple power-up; it is a profound and often painful journey of rediscovery. When he regains his sense of pain, his sense of hearing, or his voice, he is overwhelmed by new and confusing sensations, making him initially more vulnerable. His mission is a desperate struggle to become fully human, a goal that puts him on a direct collision course with his own family, who rule the prosperous lands built upon his suffering.

His role in the story as a demon-slayer is complicated by the presence of his traveling companion, a young thief named Dororo. Dororo attaches himself to Hyakkimaru after being saved from a demon, and despite their contrasting natures, a deep bond develops. Dororo acts as his guide to the human world, explaining social customs, procuring food, and providing vocal commentary on the injustices they witness. In turn, Hyakkimaru develops a powerful, protective instinct towards Dororo, becoming a fearsome guardian whenever the child is threatened. This relationship is the primary catalyst for his emotional development, slowly introducing concepts like friendship, trust, and compassion into his previously empty world.

Key relationships define his path. Dr. Jukai is his true father, the man who gave him a chance at life and taught him to fight, and Hyakkimaru holds deep, silent gratitude for him. In stark contrast, his biological father, Daigo Kagemitsu, is his arch-enemy, a man Hyakkimaru vows to kill upon learning the truth of his sacrifice. His relationship with his mother, Nui No Kata, and his younger brother, Tahomaru, is tragic. He feels little connection to them initially, but their interactions are fraught with the pain of a family broken by a cursed pact. Another significant figure is Mio, a young woman who cares for war orphans. Her kindness and tragic death awaken a deep well of rage and grief in Hyakkimaru, representing a major turning point in his emotional journey.

Throughout the narrative, Hyakkimaru undergoes significant development. He transforms from an emotionless, unstoppable killer of demons into a more complex, vulnerable, and truly human individual. As he regains his senses, he experiences the world with a childlike wonder, but also learns the burdens of pain, sorrow, and the moral weight of his actions. He is forced to confront the consequences of his quest, realizing that by killing the demons, he is destroying the source of his father's prosperity and bringing suffering to the innocent people of his homeland. His journey becomes not just about reclaiming his body, but about deciding what kind of person he wants to be with it, culminating in a final choice that prioritizes his humanity over simple revenge. He earns his happy ending, regaining his full body and setting off to discover what it means to live as a whole person.

Hyakkimaru's notable abilities are intricately tied to his disability and his curse. His primary power is his extrasensory perception, which allows him to see the souls of all living things and "hear" the sound of a demon's presence. He is an extraordinarily skilled swordsman, his fighting style honed by a lifetime of relying on instinct and spiritual awareness rather than sight. His prosthetic limbs are also weaponized; he has swords in his arms, and his leg could be equipped to spray caustic liquids. Furthermore, he demonstrates superhuman physical characteristics, including impressive speed, agility, and strength, likely a byproduct of his cursed origin. As he defeats demons and regains his true body parts, his abilities shift from being that of a near-invincible, painless killing machine to a more balanced, though still formidable, human warrior who must learn to fight with the vulnerabilities of real flesh and blood.