Hiroki Hanzawa is a detective affiliated with law enforcement who maintains staunch skepticism towards supernatural phenomena. His inherent power of disbelief extends into a deep-seated distrust of fellow human beings. This trait draws the attention of the exorcist Rihito Hiyakawa, forging a professional yet complex association between them. Hanzawa possesses a unique investigative aptitude described as an ability to "sniff out crime," aiding his police work.

He holds exclusive knowledge of Hiyakawa's horrific past, specifically his involvement in the mass murder of a cult, and played a role in assisting Hiyakawa afterward. Despite overt skepticism about the supernatural, Hanzawa repeatedly seeks Hiyakawa's assistance on unsolvable cases, demonstrating pragmatic recognition of Hiyakawa's abilities. An underlying protectiveness or soft spot for Hiyakawa exists beneath his rough professional demeanor. During investigations, Hanzawa begins suspecting connections between Hiyakawa's traumatic history and their current cases.

Physically, Hanzawa is an adult male with black hair, grey eyes, and noticeable eye bags, typically seen wearing a suit. His personality blends a cool, composed exterior during investigations with a fundamentally cynical worldview.