Nano, originally Nicole Premier, emerged from Project Nicole—a military genetic engineering program designed to craft the perfect human weapon. Selected as a child test subject, he underwent procedures suppressing his emotions and augmenting his physical prowess. His blood became the source of Line, a performance-enhancing drug circulated in Toshima. During a facility breakout, he killed nearly all researchers—sparing only Emma, who had shown him kindness—and eliminated multiple test subjects, including Motomi's son. After escaping, he vanished before resurfacing in Toshima.

He exhibits superhuman speed and strength, enabling movements perceived as teleportation. Nano demonstrates a tranquilizing hypnotic effect, allowing him to move unseen by individuals like Akira and Takeru. He can forcibly transfer his own emotions, such as grief or despair, to others. His combat methods involve spearing human bodies with his hands and utilizing improvised projectiles. Enhanced Line, derived from his blood, grants users temporary power boosts, though its purity proves lethal if ingested directly by ordinary humans.

Genetically manipulated into emotional detachment, Nano maintains a stoic and enigmatic demeanor, rarely reacting even when injured. Gaps in his worldly knowledge, stemming from his confined upbringing, manifest in actions like attempting to eat tree bark or biting into packaged Solids without removing wrappers. He views fate as immutable, often expressing this through riddles during encounters. Despite apparent apathy, he exhibits curiosity about human connections, particularly with Akira, whom he repeatedly seeks out. His actions suggest an internal conflict between his weaponized nature and residual humanity.

He maintains complex ties with key figures. Nano feels an unexplained bond with Akira, intervening to save him multiple times. His relationship with Emma involves lingering affection from their lab past, though she later seeks to kill him to end his suffering. Shiki, whom Nano spared during a battlefield encounter, aims to kill him to erase lingering dread. Motomi intends to kill Nano to halt military research, not for revenge. Nano coordinates Line distribution with Shiki but remains distrustful of him.

Throughout the series, Nano appears as a cryptic observer on Toshima's rooftops, often accompanied by cats. He leaves Line vials for participants and directly influences events—supplying Takeru with Line or tasking Akira with delivering a case to Shiki. In the anime, he rescues Akira and Keisuke from Gunji, leading to a confrontation where Emma reveals Akira's role as Line's antidote and Nano's history. His final clash with Shiki culminates in Shiki drinking Nano's blood for power, resulting in Nano's defeat. He subsequently helps Akira and Rin escape Toshima before facing soldiers alone.

In the manga, Nano frequently aids Akira—returning his lost knife, catching him during a fall, and sheltering him in a greenhouse. He engages in prolonged battles with executioner Gunji, ultimately killing him with his own weapon. Flashbacks depict his lab experiences and combat efficiency, annihilating enemy troops in minutes. His route in the game serves as the concluding narrative, requiring completion of all other routes first. Here, his interactions with Akira deepen, involving riddles, shared meals, and an electric sensation from physical contact. He rescues Akira and Keisuke after their rain-soaked battle.