Dogusaburō Oniyama is the head of the police department’s anti-phantom thief bureau, a forty-two-year-old inspector whose entire professional identity is built upon the singular goal of capturing the elusive phantom thief Joker. His dedication to this pursuit is so absolute that he is willing to chase his quarry outside of Japan, traveling internationally for any opportunity to make an arrest. Physically, Oniyama has a distinctive and somewhat comical appearance, featuring a long, thin mustache, a prominent bald patch on the crown of his head, and long black hair that is brushed out from the sides. He also has a noticeable mole positioned between his eyes and sharp, pointed teeth. His standard attire is a consistent and recognizable parrot green suit, paired with a black tie and black shoes.

Despite his high rank and authority, Oniyama’s relentless efforts to apprehend Joker almost always end in spectacular and comical failure, with the phantom thief consistently outmaneuvering his elaborate traps and security measures. However, the inspector’s character is more nuanced than a simple obsession. In moments of genuine crisis, particularly when innocent lives are at stake, he will grudgingly set aside his enmity and cooperate with Joker. This is most evident when his daughter, Haruka Oniyama, is put in danger; on such occasions, his distress overrides his professional hatred, and he demonstrates a deep and genuine capacity for care and concern for his family. This dynamic extends to his home life, where he is known to be unable to defy the wishes of his wife, Tomoe Oniyama, and his daughter, often finding himself dragged along on shopping trips during his days off.

In his professional role, Oniyama leads a team that includes his subordinates, Ginko Kurosaki and Momo Shirai, in a seemingly endless campaign to thwart Joker’s heists. While his fixation on Joker is a source of constant frustration, it also defines his very purpose. The depth of his obsession is such that when Joker is temporarily captured, Oniyama does not experience the triumph he expected; instead, he becomes melancholic, listless, and loses all energy, even going so far as to draft a letter of resignation from the police force. The moment he learns of Joker’s inevitable escape, he is instantly revitalized, tearing up the letter with renewed energy and happiness. This complex relationship forms the core of his role in the story, transforming him from a mere secondary antagonist into a rival whose grudging respect for Joker is earned through the phantom thief’s strong morals and unwavering commitment to his own code of justice.