In the original No.6 novels, Nezumi is described as having a pale, fair complexion and a slender jawline, contributing to an androgynous and somewhat feminine appearance. He has sharp gray eyes and black hair, which appears dark gray in the anime. Shion notes that while Nezumi maintains a lean and agile frame, his broad shoulders and toned musculature reflect hidden strength. A large burn scar roughly the size of a human hand marks his back, a remnant of a traumatic event from his childhood. In the anime adaptation, Nezumi is shown to have multiple burn scars across his body.

Nezumi’s outfit typically consists of a dark gray, green-tinted leather jacket adorned with zippers and pockets. Beneath the jacket, he wears a pale yellow long-sleeve shirt. His beige cargo pants are similarly rugged, featuring large side pockets. He wears his pants asymmetrically tucking the left leg into a combat boot while leaving the right leg loose and tattered. A prominent feature of his attire is the large, dark gray scarf made of superfiber cloth, which also functions as a cloak due to its durability and size.

In both the manga and anime adaptations, Nezumi’s hairstyle differs from the novels. His hair is longer, extending to his shoulder blades, and is usually styled in a high spiked ponytail, often tied with a strand of his own hair. In the anime, his hair is depicted with a slate-gray tone instead of black.

At age twelve, Nezumi had shoulder-length hair and wore a simple light gray sweater with rolled-up sleeves and denim blue shorts. At the time, he was notably shorter than Shion.

Nezumi is initially portrayed as a cold, sarcastic, and sharp tongued individual with a strong aversion to personal questions or emotional vulnerability. He is quick to become irritable, often responding with hostility when Shion or anyone else pries into his past. His interactions are frequently laced with cynicism, condescension, or mockery, particularly toward those affiliated with No.6. This aloofness masks a deeply guarded emotional core shaped by trauma and distrust.

Despite his abrasive behavior, Nezumi is capable of surprising kindness and empathy, even if he rarely acknowledges it. He demonstrates a protective streak toward those he cares about especially Shion and performs small, thoughtful gestures in secret, such as gifting Shion’s sweater to a young girl named Karan. These moments hint at the compassion beneath his hardened exterior.

Nezumi is also highly intellectual and theatrical, with a pronounced love for classic literature, particularly the works of Shakespeare. His room is cluttered with books spanning various topics, including literature, ecology, and scientific journals. Though lacking formal education, he possesses an exceptional breadth of knowledge. However, he is disorganized in his living habits, something frequently noted by Shion, and his home reflects his chaotic yet rich inner world.

In addition to his book smarts, Nezumi is a skilled survivalist with sharp instincts and quick reflexes. He is resourceful in combat, adept at infiltration, and capable of making morally ambiguous decisions to achieve his goals as seen when he tortures a No.6 official, Fura, for information.

Throughout the series, Nezumi undergoes significant character development. In the beginning, he staunchly believes that emotional attachments and memories are shackles that lead to suffering. However, as his relationship with Shion deepens, this ideology gradually unravels. Nezumi becomes increasingly protective and affectionate, often placing Shion’s safety above his own. In the anime, there is a moment where he nearly confesses to “falling in love” with Shion, though he is interrupted during a tense infiltration mission. Similar emotionally charged moments are depicted in both the manga and the novels, strongly implying romantic feelings that Nezumi struggles to express directly.

Nezumi is a descendant of the Forest Folk, an ancient and peaceful race who lived in Mao Forest long before much of the planet was ravaged by war. The Forest People lived in deep harmony with nature communing with the wind, earth, rivers, and sky and possessed the rare ability to communicate with animals and the forest itself. Among them were gifted individuals known as “Singers,” who could reach and appease Elyurias, a powerful being, through song. Nezumi inherited this rare ability.

In ancient times, the Forest Folk made a pact with Elyurias to avoid being turned into hosts for her parasitic wasps. In exchange, they offered her a vessel called the “Godly Bed,” a nest constructed from animal brains where Elyurias could safely lay her eggs. The Forest People vowed to guard this nest with their hearts and souls through the generations, maintaining a sacred balance that kept the parasitic threat at bay.

However, the city-state of No.6, seeking to exploit the parasitic wasps for their ability to control human hosts, launched an invasion of Mao Forest. The Forest Folk resisted, but the technological and militarized forces of No.6 proved overwhelming. In what became known as the “Mao Massacre,” the Godly Bed was seized, the forest was burned to the ground, and nearly all of Nezumi’s people were slaughtered.

At just five years old, Nezumi witnessed the destruction of his homeland and the deaths of his family and community. During his escape, he suffered severe burn injuries to his back. His survival was due to an elderly woman, whom he affectionately referred to as “Gran,” who carried him to safety and raised him in secret. Gran harbored a deep hatred for No.6 and passed this resentment on to Nezumi. She eventually attempted to assassinate the Mayor of No.6 but was killed in the process. Following her death, Nezumi was captured and imprisoned in the Correctional Facility, where he was left to die in its basement.

There, he encountered Rou, a man who lived in the underground tunnels below the city. Rou took Nezumi in and taught him how to survive, eventually devising a plan to help him escape. He informed authorities that Nezumi was the last surviving member of the Forest Folk and suggested they could gain significant value by delivering him to the Moondrop facility for experimentation. Before parting, Rou gave Nezumi a knife and instructed him to flee at the first opportunity.

While being transported to the Moondrop, Nezumi fabricated a story, claiming he had always wanted to hear the Moondrop “howl” and begged to witness it one last time before becoming a test subject. When the security personnel lowered their guard, Nezumi took the opportunity to escape into the sewers, narrowly evading capture by the Security Bureau.

His escape eventually led him into Shion’s life, setting the course for the events that would unfold as both boys began uncovering the dark truths hidden within No.6.

Nezumi possesses a wide range of physical, mental, and mystical abilities that make him a formidable and resourceful character. He is highly intelligent and instinctive, with an animal-like ability to sense danger, allowing him to anticipate threats and navigate hostile environments with ease. His agility and physical strength are notable evident in his survival of the harsh conditions within the Correctional Facility and his ability to evade and outmaneuver trained enforcers from No.6.

He is highly proficient in hand-to-hand combat and excels in the use of a combat knife, which he frequently carries. Nezumi also demonstrates competency with firearms, though he prefers close-quarters combat and stealth tactics.

In addition to his physical skills, Nezumi holds a rare and mystical heritage. According to the novels, he is the last known Singer of the Mao Forest Folk individuals capable of communicating with Elyurias through song. This ability grants him influence over Elyurias, a being connected to the parasitic wasps central to the story’s conflict. His singing voice is described as ethereal and haunting; Inukashi, also known as the Dogkeeper, remarks that Nezumi’s voice has the power to “carry away the soul without pain,” hinting at its otherworldly, almost spiritual quality.

Nezumi’s blend of survival instincts, combat prowess, intellectual depth, and mystical heritage makes him one of the most complex and capable characters within the No.6 universe.

Shion
Nezumi first encountered Shion during a stormy night when he broke into his home seeking refuge from the authorities. Despite being a complete stranger and a fugitive with a gunshot wound Shion offered to treat his injury without hesitation. This unexpected act of kindness left a lasting impression on Nezumi. As the two spoke, Nezumi openly criticized No.6 as a brainwashing project disguised as a utopia. To his surprise, Shion readily agreed with him, showing an unusual openness and clarity of thought for someone raised in the system.

Over time, Nezumi developed deep and complex feelings for Shion. While he often criticizes Shion’s idealism especially his refusal to resort to violence Nezumi clearly admires his compassion and unwavering hope for a better world. Their relationship is filled with tension, mutual protection, and emotional vulnerability. Several moments throughout the series strongly suggest romantic feelings between them. For example, in episode 7 of the anime, Shion gives Nezumi what he calls a “goodnight kiss,” which is later revealed to be a “goodbye kiss” and a thank-you.

Nezumi is also protective of Shion’s innocence and deeply affected by his suffering. This is shown when Shion kills a guard in defense of Nezumi, a moment that causes Nezumi to weep, believing he forced Shion to cross a line. Despite his belief that survival should come above all else, Nezumi chooses to remain behind in the collapsing Correctional Facility to sing for Shion’s soul after he is shot, illustrating just how much he values him. In episode 10, Nezumi quietly says, “I have fallen,” while thinking of Shion, an ambiguous but emotionally charged statement. In the anime’s final episode, Nezumi kisses Shion and promises they will meet again, further solidifying the romantic undertone of their bond.

Inukashi
Nezumi and Inukashi share a hostile yet functional relationship. Their initial meeting was confrontational Inukashi broke into Nezumi’s underground home looking for resources, only to be caught and threatened. Despite their animosity, the two rely on each other professionally. Nezumi depends on Inukashi’s information network, while Inukashi trusts that Nezumi will keep his word when making deals.

Though they often bicker and provoke one another, their shared connection with Shion gradually forces them into a fragile cooperation. Inukashi once remarked that if they were ever dying, they’d want Nezumi to sing for them, a testament to the grudging trust and strange sense of mutual respect between them.