Kazuya Shibuya, also known as Naru, serves as the 17-year-old manager of Shibuya Psychic Research (SPR). He initially presents as a Japanese researcher, but his true identity is Oliver Davis, a prominent British paranormal investigator and psychic. He operates under the alias "Kazuya Shibuya," taken from his Tokyo office location. The nickname "Naru" originates from Mai Taniyama, referencing his narcissistic demeanor, and becomes widely adopted by colleagues. This nickname notably resembles his childhood nickname "Noll," causing initial confusion when Mai uses it.

Physically, he is tall with short black hair and dark-indigo eyes. His consistent attire is entirely black, featuring a high-collared long coat, turtleneck shirt, scarf, pants, and shoes.

His personality is cold, analytical, and highly critical, with little tolerance for weakness in himself or others. Despite this reserve, he demonstrates genuine respect for individual talents and harbors deep concern for his team's well-being, earning their trust. He exhibits competitiveness, particularly in dismantling fraudulent paranormal activities, but avoids pointless rivalries. Mai Taniyama uniquely challenges his authority openly, which he finds intriguing rather than irritating. He rarely displays emotions openly, though subtle mood shifts can cause noticeable drops in room temperature, unnerving those nearby.

His background reveals he and his identical twin brother, Eugene (Gene), were orphaned and adopted by paranormal researchers Martin and Luella Davis in England. The brothers shared an exceptionally strong psychic connection, with Gene acting as an amplifier for Kazuya's immense psychokinetic (PK) energy, enabling safer ability use. After Gene's death—experienced via psychometry revealing a hit-and-run in Japan and disposal in a lake—Kazuya traveled to Japan to find his brother's body and investigate his death, leading to the establishment of SPR's Japanese branch.

Kazuya possesses formidable psychic abilities: powerful psychometry and extraordinary PK strength. However, using his PK without Gene to regulate it places severe physical strain on him, risking unconsciousness or heart failure, restricting its use to dire emergencies. Lin Koujo, his childhood friend and assistant, taught him Qigong to help manage his energy, though its use remains hazardous. Professionally, Kazuya approaches paranormal investigation with rigorous scientific methodology, employing extensive technology like cameras and sensors, and advocates for treating psychic research as a science to gain credibility. He initially conceals his own psychic capabilities from his team.

His relationships are complex. He employs Mai Taniyama ostensibly to repay a broken camera (though it was insured); the real reason involves empathy for her orphaned status, mirroring his own. While frequently criticizing her lack of paranormal knowledge, he consistently trusts her instincts and latent psychic abilities during cases. He treats her distinctly: addressing her solely by her first name without honorifics, showing patience with her criticisms, occasionally comforting her in peril, and displaying subtle gestures like gentle forehead touches despite a general aversion to physical contact. He is also observed to genuinely smile only in her presence. These actions, alongside author Fuyumi Ono's confirmation of mutual romantic feelings, indicate deeper regard. However, Gene's appearance in Mai's dreams complicates their relationship, leading Kazuya to question whether her eventual confession is for him or his brother.

Lin Koujo, his steadfast assistant, guardian, and childhood friend of both twins, provides crucial support as an onmyouji. Despite initial friction from Lin's historical resentment towards Japanese people, their relationship evolves into profound mutual respect. Kazuya maintains professional relationships with other SPR consultants like Buddhist monk Houshou Takigawa and celebrity medium Masako Hara, the latter leveraging early knowledge of his true identity. He navigates team dynamics strategically, often relying on Takigawa for leadership in his absence.

Significant development occurs as he transitions from a solitary investigator to a leader valuing his team, demonstrating underlying loyalty and protectiveness, especially towards Mai. Resolving Gene's case allows him to begin processing his grief, though he returns to Japan to continue SPR's work. Key moments illustrating his care include risking his health using PK to save Mai during the "After School Hexer" case, resulting in hospitalization, and his complex emotional response to Mai's confession amidst his brother's lingering shadow.

Trivia notes include his favorite drink being black tea and the temperature fluctuations associated with his mood shifts.