Dogusaburō Oniyama commands the police anti-phantom thief bureau, obsessively dedicated to capturing phantom thief Joker. He sports a bald patch, long black hair swept to the sides, a mole between his eyes, sharp teeth, and a signature parrot green suit with black tie and shoes. Racing across global heists, his relentless pursuit of Joker consistently fails or backfires comically. Despite this, he adheres to strong moral principles, preferring fair capture over underhanded tactics, earning Joker's respect.

Oniyama cherishes his family: wife Tomoe and daughter Haruka. He demonstrates intense care, particularly for Haruka, becoming distraught after her kidnapping in Episode 22 and reluctantly collaborating with Joker to save her, even negotiating an exchange of the "Tiger in the Moonlight" scroll for Joker's aid. His dynamic with Joker transcends rivalry; Oniyama shows genuine concern when Joker faces mortal peril, like poisoning or missiles, while Joker trusts him to apprehend defeated criminals like Dr. Neo and Sniper Genma.

His character deepens as obsession with capturing Joker leads to depression upon Joker's imprisonment, only revitalized by Joker's escape. An ESTJ personality drives his structured, duty-bound approach, tempered by moments of compassion. He leads junior officers Ginko Kurosaki and Momo Shirai in operations and partners directly with Joker during critical events like neutralizing the Wicked Foxes or resolving a theme park hostage crisis.

Evolving from secondary antagonist across all seasons, Oniyama emerges as a nuanced figure defined by dedication to justice and a complex rapport with Joker. His surname subtly echoes the Japanese yōkai "oni," reflecting his fierce, occasionally misguided determination.