Kazuya Shibuya, operating primarily under the nickname "Naru," manages and leads investigations at Shibuya Psychic Research (SPR). He presents as a 17-year-old Japanese researcher but is secretly Oliver Davis, a renowned British paranormal expert. The alias "Kazuya Shibuya" references his Tokyo office location, while the nickname "Naru," coined by Mai Taniyama for his perceived narcissism, becomes his common identifier among colleagues. This name also phonetically echoes "Noll," a childhood nickname used by his identical twin brother, Eugene Davis.

Naru exhibits an analytical, reserved, and intellectually driven personality. He displays minimal tolerance for inefficiency or emotional displays, maintaining a consistently stoic and detached demeanor. Despite this, he possesses genuine respect for individual talents and a strong competitive streak, particularly against fraudulent paranormal practitioners or threats to his team. His leadership prioritizes logic and scientific methodology, though he selectively acknowledges intuitive insights, especially Mai's. Ambient temperatures noticeably drop during moments of his intense irritation or concentration.

His past is marked by tragedy. Orphaned alongside his twin Gene, they were adopted by the prominent Davis paranormal research family. The twins shared an exceptionally strong psychic bond. Naru psychometrically experienced Gene's death—a hit-and-run in Japan followed by disposal in a lake. This drove Naru, as Oliver Davis, to establish SPR in Japan, primarily to locate Gene's body and uncover the truth behind his death. Childhood training under Lin Koujo in qigong helped him manage volatile psychic energies, overcoming initial ethnic tensions to forge deep mutual respect.

Naru wields formidable psychic abilities: potent psychokinesis (PK) and psychometry. Using PK requires extreme caution. Historically, Gene acted as amplifier and regulator for Naru's power. After Gene's death, employing PK causes severe physical strain, risking unconsciousness, heart failure, or extended hospitalization, as seen when moving rubble to save Mai or confronting powerful entities. Consequently, he relies heavily on technology and his SPR team's specialized skills, reserving his own powers for critical emergencies. His scientific approach to the paranormal is documented under his real name, Oliver Davis.

His relationship with Mai Taniyama forms a central dynamic. He hires her ostensibly to repay a broken camera (which was insured); his true motivation stems from empathy, knowing she is an orphan like himself. While frequently critical of her inexperience, he uniquely addresses her by her first name without honorifics, tolerates her challenges to his authority, and consistently protects her during investigations. Subtle indications of romantic interest exist, including rare genuine smiles directed solely at her and physical contact despite his general aversion to touch. When Mai confesses her feelings, he questions if her affection is meant for him or Gene, who appears in her dreams. The series' author confirmed mutual romantic feelings exist but intentionally left the relationship unresolved.

Professional relationships define his interactions with the SPR team. Lin Koujo serves as his primary assistant and most trusted confidant, handling complex rituals and providing protection due to Naru's vulnerability when using his powers. He defers to Lin's expertise in onmyoudo despite Lin's initial resentment towards Japanese people. With other members—Houshou Takigawa (Monk), Ayako Matsuzaki, John Brown, and Masako Hara—Naru maintains a primarily professional, sometimes brusque, dynamic, valuing their specific skills while keeping personal distance. Masako Hara alone learns his true identity early and leverages this knowledge.

Following Gene's funeral, Naru returns to Japan with Lin, citing the country's heightened supernatural activity as the reason to continue SPR's operations. Trivia notes include his preference for black tea and the origin of his office name.