Koichi Zenigata is an inspector for Interpol whose life and career are defined by his relentless pursuit of the master thief Arsene Lupin III. Originally an officer in the Tokyo Metropolitan Police Department, he transferred to Interpol specifically to dedicate himself entirely to this single case, a mission that has consumed him completely and left little room for any other aspect of life, such as family or personal relationships.

In the television special Lupin III: Missed by a Dollar, Zenigata is confronted with the potential end of his life's work. When circumstances lead him to believe that Lupin has died, he suffers a profound crisis, losing the very purpose that drives him. This despair is so deep that it causes him to abandon his post and resign from Interpol, demonstrating that his identity is inextricably linked to his role as Lupin's pursuer. The eventual reappearance of Lupin, alive and well, restores his drive and passion, allowing the familiar and vital dynamic of their rivalry to resume. This specific story highlights the dependency of his sense of self on the chase itself.

Zenigata's personality is a complex mix of high competence and sincere vulnerability. He is a highly skilled detective, often managing to deduce Lupin's plans and consistently tracking him down across the globe. Despite this capability, he is frequently outwitted by his quarry, leading to a public persona that can be seen as bumbling. His obsession, however, hides a deep sensitivity. He is prone to emotional outbursts, particularly when his adversary performs an unexpected act of kindness or when the fate of Lupin is in question. This sensitivity does not undermine his determination; rather, it reinforces the very personal and emotional nature of his hunt. His motivations are singular and unwavering. Zenigata is not primarily driven by a general desire to enforce the law but by a burning, personal need to be the one to finally put handcuffs on Lupin III. This intense focus often makes him overlook other criminals and the rest of Lupin's gang when the master thief himself is present. His refusal to let anyone else capture or kill Lupin creates a strange, protective dynamic within their intense rivalry.

The relationship between Zenigata and Lupin is the central axis of his character. In Missed by a Dollar, this bond is pushed to its limit. His collapse at the thought of Lupin's death and his subsequent resurrection of purpose highlight the symbiotic nature of their connection. He acts as a foil who represents law and order, yet his personal code and grudging respect for his nemesis make him an integral part of the heist narrative. He cannot find peace or pursue other ambitions until his goal is fulfilled, making his inability to catch Lupin both a professional failure and a tragic source of meaning. Zenigata is known for his incredible endurance and physical resilience, often surviving dangerous situations in his tireless chase. His signature method of capture involves a pair of handcuffs attached to a rope, which he throws with remarkable accuracy to apprehend suspects from a distance. He is also proficient in martial arts and a capable hand-to-hand combatant, though his skills are consistently tested against the superior resources and elaborate schemes of his target.