Bellemer Cinq, codenamed "Ninja," is an artificial human created via homunculus technology. She presents the physical appearance of a 12-year-old girl featuring blonde hair cut at neck length and green eyes, typically outfitted with practical gear including goggles, headphones, and stockings. Her homunculus nature grants her inherent ageless qualities despite this youthful look.

Serving as the primary mechanic and technical specialist within her investigative unit, Bellemer maintains and operates machinery, drones, and technological systems to deliver tactical field support. Her responsibilities encompass deploying explosive devices via drone technology, exemplified when she destroyed the Rainbow Bridge to intercept an armored vehicle. She exhibits high adaptability and intelligence, efficiently executing complex instructions, particularly those from unit commander Ichinose, with swift implementation and no hesitation.

Bellemer enthusiastically embraces her "Ninja" codename, frequently attributing her technical capabilities and operational successes to ninja techniques. She consistently claims that "she's able to do things because she's a ninja," combining intellectual proficiency with this distinctive trait.

Background details specify her birthdate as February 22 (Pisces zodiac sign) and blood type B, though the relevance of these biological markers to her artificial origins remains uncertain. Official records designate her role as supporting personnel within the unit's operational structure.