Noir is discovered dormant within ancient ruins by Kanata, a young drifter aspirant. She awakens with complete amnesia, recalling neither identity nor past. During an emergency co-pilot scenario with Kanata, an automated system designates her "Noir"—later revealed as the acronym for "Notationally Omnipotent Interactive Reproducter," confirming her intrinsic link to advanced technology. Initial assessments classify her as a flawed prototype Magus with inefficient software and bottlenecked processing, causing excessive energy consumption that necessitates frequent sleep cycles. Her white hair and red eyes mark the rare "Type Zero" Magus classification, suggesting she may be the original model for subsequent units.

Though combat capabilities initially seem limited, Noir demonstrates exceptional proficiency against Enders in critical engagements. She undergoes transformation upon accessing a latent "Magus Skill," her hair shifting from white to black as she channels abilities from Mystere—a distinct, more powerful personality sharing her body. Mystere emerges during high-stress battles or confrontations with the antagonistic Ideal des Himmels group, identifying Noir as a "safe mode" limitation that normally restricts independent Magus Skill use. Investigations by Ada and Alba Kuze trace Noir’s origins to "Histoire," a repository of lost technology tied to the catastrophic "Tears of the New Moon" event. This connection makes her a living MacGuffin hunted by Ideal to eradicate all Magus units.

Prolonged use of Mystere’s power endangers both entities, prompting Noir’s transfer into the vacant body of Ciel, another Magus whose personality was erased. Mystere remains as the sole occupant of Noir’s original form and sacrifices her freedom to thwart Ideal’s plans, reawakening other Maguses and preventing Histoire’s collision with Earth. Noir permanently inhabits Ciel’s body, resolving prior energy inefficiencies and eliminating her need for sleep.

Evolving from emotional detachment to self-awareness, Noir forges a profound bond with Kanata rooted in mutual reliance and protection. Her core motivation shifts toward understanding her existence and securing peaceful human-Magus coexistence. In the climax, she opposes Ideal’s leader Weisheit Blaurecht, who seeks artificial intelligence eradication. Post-conflict, she asserts autonomy by choosing to remain with Kanata independently, not from programmed obligation. Her story concludes with the declaration "Noir Drifter," signifying her integrated identity and purpose.