Gonzo Tarukane is a minor but memorable antagonist from the Spirit Detective Saga, serving as the final human villain of that story arc. He is a grotesquely obese and incredibly wealthy businessman whose fortune is said to surpass the annual revenue of entire countries. His physical appearance is notably unappealing; he is short and dumpy with a large stomach, no visible neck, sagging wrinkled cheeks, massive protruding lips, wide droopy eyes, and a large button-shaped bump on his otherwise bald head. Despite his vulgar appearance, he consistently wears lavish formal business attire, typically a royal purple suit with a red tie, and is often seen with an unlit cigar in his mouth.

Tarukane's personality is defined by extreme greed, cowardice, and cruelty. As a multi-trillionaire, his primary motivation is the relentless accumulation of even more wealth, which he pursues through any dishonorable means available on the black market. He possesses no respect for the lives or suffering of others, whether human or demon, viewing them only as tools for profit. This is most clearly demonstrated by his treatment of the ice apparition Yukina, whom he holds prisoner. He subjects her to various forms of torture specifically to force her to cry, as her tears magically crystallize into valuable jewels. He is portrayed as overconfident and short-tempered, believing his immense riches can insulate him from any consequence. In the English dub of the anime, his characterization is expanded; he is identified as the founder of the Black Black Club, a secretive and sadistic organization responsible for the capture, enslavement, torture, and murder of countless innocent demons for entertainment and profit, making his villainy significantly more far-reaching.

In the story, Tarukane serves as the chief obstacle in the mission to rescue Yukina. After his own guards and torture methods fail to produce tears from the resilient ice maiden, he hires the legendary Toguro Brothers to break her will. The brothers succeed by callously killing two small birds in front of her, which triggers her tears of sorrow. When Yusuke Urameshi and his friends infiltrate his mansion to free Yukina, Tarukane responds not by fighting, but by organizing a series of high-stakes bets with his fellow Black Black Club members via a video conference. He wagers vast sums of money on his hired demons defeating the young intruders. This gambling scheme reveals his arrogance and his belief that his fortune can solve any problem.

The most significant relationship Tarukane has is with the Toguro Brothers, specifically the younger brother. Tarukane hires them as muscle, believing his money ensures their absolute loyalty. In an attempt to intimidate Younger Toguro, he unveils a massive, genetically engineered four-legged beast named Helen, boasting of its destructive power. When Toguro nonchalantly accepts a challenge to fight the creature and effortlessly kills it with only thirty percent of his strength, Tarukane is stunned but also sees a new opportunity to hustle his associates. Unbeknownst to Tarukane, Younger Toguro has already been hired by another club member, the enigmatic Sakyo, to deliberately lose the final bet. Tarukane remains completely unaware that he is being manipulated as a pawn in a larger scheme to bankrupt him. His relationship with Yukina is purely that of an abuser to a victim, showing no empathy and expressing bafflement that she would care about the deaths of birds. He also interacts with the intruders, mainly by watching from a monitor as his bets fail one by one.

Tarukane undergoes no redemption or positive development. As his schemes collapse and Sakyo reveals that his final, massive wager on the intruders has cost Tarukane his entire fortune, the villain's true cowardice emerges. He abandons all pretense and tries to flee his own mansion with Yukina. He is stopped by Hiei, who is Yukina's long-lost brother. Hiei brutally beats Tarukane, but Yukina stops him from delivering the final blow, stating that his death would only cause her more pain and not undo his crimes. Hiei spares him, declaring Tarukane is not even worth killing. Tarukane is last seen babbling to himself, bloody and broken. His ultimate fate is sealed not by the heroes, but by his own hirelings. The Toguro Brothers reveal their betrayal, and on Sakyo's orders, Younger Toguro decapitates Tarukane with a single, powerful kick, disposing of him as a useless and bankrupt pawn.

Regarding notable abilities, Gonzo Tarukane possesses no supernatural powers, spiritual awareness, or notable combat skills. He is, in every sense, a non-combatant. His only strengths are his immense financial wealth, which allows him to hire powerful demonic mercenaries, and his ruthless cunning in manipulating the black market and gambling rings. His true influence is derived from his money and the corrupt organizations he controls or belongs to, not from any personal physical or spiritual power.