At the age of twelve, Shion is depicted wearing a white dress shirt layered with a light turquoise sweater vest, paired with light brown trousers and dark brown shoes. As a resident of No.6, he also wears the city’s official identification bracelet on his left wrist. Originally, Shion had soft brown hair and matching brown eyes.

However, following an incident involving a parasitic wasp, Shion undergoes a dramatic physical transformation. His hair turns white, and his eyes become a vivid violet though they appear red in the manga and anime adaptations. Additionally, he develops a long, pinkish red scar that spirals across his body. In the manga and anime, the scar runs from his left ankle up to his left cheek, just below the eye. In the novel, the scar wraps around his entire body in a chaotic pattern up to his neck, as if emerging from within his veins.

Shion has a slim physique, though not severely underweight. In later appearances, he is seen wearing black trousers and a distinctive red coat with a hood. Beneath it, he dons a white collared shirt layered with the same light turquoise sweater, maintaining a consistent visual link to his past self.

Shion is portrayed as a kind-hearted and compassionate individual, often guided by his strong sense of empathy and idealism. He exhibits a deep care for others and maintains a generally optimistic worldview, even in the face of the dystopian realities surrounding him. His intelligence is exceptional demonstrated by his acceptance into No.6’s prestigious Special Course and his ability to successfully treat and suture Nezumi’s gunshot wound at the age of twelve. His curiosity often outweighs fear, as shown when he remains fascinated rather than frightened by Nezumi’s threatening behavior early in their acquaintance.

Despite his gentle nature, Shion displays a hidden, darker side when those he loves are endangered. Though slow to anger, he is capable of violence in moments of extreme emotional stress. This is seen when he strikes Rikiga for insulting Nezumi, attempts to strangle Sasori during a confrontation in the cave, and fatally shoots a guard who had gravely injured Nezumi. Each of these instances reveals a more aggressive and almost unrecognizable side of Shion, often followed by visible shock or regret over his own actions.

While the anime and manga only hint at this duality, the novels explore it in greater depth. Nezumi admits he fears this hidden side of Shion, and Inukashi also senses a latent intensity within him. Sasori even refers to Shion as a “demon” during their clash, underscoring the unsettling transformation he undergoes when pushed to his limits.

Though initially grateful for the life he led in No.6, Shion harbors quiet doubts about the city’s perfection. He gradually becomes disillusioned with its rigid control and hidden injustices, largely influenced by Nezumi’s worldview. Shion is also shown to be insecure about his physical appearance, particularly his slender frame, and tends to daydream. He shares a strong bond with his mother and values their relationship deeply.

Shion was born and raised as a privileged citizen within the elite sector of the city-state No.6. He lived with his mother, Karan, in an affluent district known as Chronos, enjoying the benefits of a system that favored intellectual and social elites. His life took a dramatic turn at the age of twelve when he provided shelter to a wounded fugitive named Nezumi. For aiding a wanted criminal, Shion was stripped of his elite status and expelled from the Special Course.

Following this incident, Shion and his mother were relocated to Lost Town, a less affluent suburban area of No.6. There, his mother opened a bakery, and Shion began working as a maintenance technician in the city park. Despite his demotion in social standing, he continued to hold onto his ideals and remained curious about the city’s deeper truths.

Shion’s defiance of the regime eventually drew further suspicion. In the anime adaptation, he is arrested for expressing doubt about the system; in the original novel and manga, he is accused of murder. He was scheduled to be transferred to a correctional facility, but was unexpectedly rescued by Nezumi, who smuggled him out of the city and brought him to his underground dwelling.

Shortly after his arrival, Shion exhibited symptoms of infection from a mysterious parasitic wasp that had begun plaguing No.6. Thanks to Nezumi’s quick intervention, the parasite was extracted before it could kill him. Although he survived, the experience left Shion with permanent physical changes, including white hair, red (or violet) eyes, and a long scar twisting across his body.

Having survived the infection, Shion became convinced that he had a responsibility to help the people of No.6 and reveal the truth behind the city’s hidden corruption. This belief set him on a path of resistance alongside Nezumi as they worked to uncover the dark secrets buried within the city’s utopian façade.

Intellect
Shion is recognized as an exceptionally intelligent individual, particularly in the fields of science and ecology. From an early age, his academic abilities set him apart, he was accepted into No.6’s elite educational program at the age of two. His deep understanding of ecological systems later proves crucial when analyzing the behavior and life cycle of the Eluyrias wasps, a parasitic species threatening the city.

Had he not lost his status for aiding Nezumi, Shion was on track to be sent outside of No.6 to pursue advanced scientific studies, marking him as one of the city’s most promising young minds. His analytical thinking, quick comprehension, and capacity to remain calm in crisis situations make him an invaluable asset in uncovering the truth behind No.6’s corrupt system.

Nezumi
Shion shares a profound and emotionally complex bond with Nezumi, the fugitive he once sheltered as a child. Their relationship is central to the narrative of No.6, marked by mutual trust, loyalty, and deep personal connection. Shion has openly stated that Nezumi means more to him than anyone else and often describes being inexplicably drawn to him. Their protectiveness of each other is intense Shion goes as far as threatening Rikiga with violence when the man implies Nezumi had been involved in prostitution.

Safu
Safu is Shion’s childhood friend and one of his closest companions during his early years in No.6. While Safu harbors romantic feelings for Shion, he does not appear to reciprocate them. Her departure to study abroad marks a turning point in the story, and she is deeply affected when Shion is expelled from the elite program.

Despite his lack of romantic interest, Shion values Safu immensely. Upon learning she has been imprisoned by the government, he willingly risks his life to infiltrate the Correctional Facility in an attempt to rescue her. Her death leaves a lasting emotional impact on Shion, adding to his disillusionment with the city of No.6.

Shion Jr.
Shion briefly becomes the guardian of a small child, later nicknamed Shion Jr., during the events inside the Correctional Facility. After rescuing the infant from a desperate mother, Shion entrusts the child to one of Inukashi’s dogs, instructing it to deliver the baby to Inukashi’s care. The child appears again after Shion and Nezumi escape the facility, symbolizing a small thread of continuity and hope amidst the chaos. In the manga’s epilogue, Nezumi has left Shion Jr. in Inukashi’s care, as noted in a letter received by Shion.