Lt. Kozo Karino operates as a detective in the Tokyo Police Department's "U" Division, dedicated to unexplained and supernatural cases. He maintains an official liaison role with Phantom Quest Corp., regularly supplying Ayaka Kisaragi with paranormal case referrals and critical intelligence. This dual position facilitates direct investigative collaboration, such as joint operations probing mysterious hospital fatalities or fraudulent exorcism rings.

Karino pursues a persistent romantic interest in Ayaka beyond their professional relationship. He attempts to demonstrate reliability through actions like independently tailing suspects or proposing police job opportunities, but frequent clumsiness undermines his efforts—his Volkswagen Beetle stalls during surveillance, and he fumbles gifts meant for her. He also intervenes to curb consequences from her impulsive drinking and spending sprees, revealing a protective streak.

Covertly perverse moments punctuate his conduct, including accidental intrusions on intimate situations or witnessing Ayaka in compromised states, typically triggering physical retaliation from her. His personality merges earnest dedication with comedic ineptitude, highlighted by ineffective gunmanship during confrontations. A recurring catchphrase—"Ms. Ayaka, are you alright?"—features in episode previews, emphasizing his consistent concern for her welfare.

Notable events include his disappearance while investigating the fraudulent Hadja monks, prompting a full Phantom Quest Corp. rescue operation. During the ensuing rooftop clash between Ayaka and monk leader Mukyo, Karino intervenes to shield her. Directors later indicated this moment held potential to advance their romantic subplot had the series extended past four episodes. No explicit background or character evolution occurs across the OVAs, light novel, or single-issue manga.