Jiro Gamo is a character from Joker Game, serving as an operative for a spy organization known as the Wind Agency. His physical appearance is characterized by brown hair that is neatly kept away from his face, which complements his matching brown eyes. He is typically dressed in a professional manner, wearing a blue suit over a white shirt, and completes this look with a dark blue tie and dark blue shoes. At first glance, he presents himself as a pleasant young man who is attentive and self-conscious about his appearance, but beneath this exterior lies a personality that is fundamentally down-to-earth and deeply serious about his work. His devotion to his assigned missions is one of his most defining traits, and he carries out his duties with a level of commitment that leaves no room for hesitation.

Within the story, Jiro Gamo initially creates a deliberate misdirection, possessing many of the same qualities as the D-Agency spies such as a ready smile and a keen mind, which makes him appear as if he could be one of their own. However, it is eventually revealed that he operates under a different philosophy entirely. While the D-Agency typically avoids killing for strategic reasons, Gamo is a member of the Wind Agency, a rival military intelligence group whose methods are far more ruthless. His personal motto, kill without hesitation, die with honor, encapsulates his core motivation and operational code, standing in stark contrast to the protagonists he initially seems to mirror. This distinction is central to his role, as he becomes a direct counterpoint to the D-Agency, representing a more traditional and brutal military approach to espionage.

Jiro Gamo is shown to be a highly capable individual, possessing intellect and skills that make him a formidable agent. Notably, he is a competitive-level chess player, demonstrating his ability for strategic thinking and complex problem-solving. One of his key missions involves infiltrating the mansion of the British consul, Ernest Graham. To achieve his objective, he manipulates the consul's Chinese butler, Chou, by first introducing him to a gambling den to get him into debt, subsequently using this debt as blackmail to force the butler to help him rob the safe. This plan illustrates his pragmatic and calculating nature. A pivotal moment in showcasing his character development and true allegiance occurs after he successfully obtains the information he needs from an entry in the consul's journal; to ensure his own silence and the mission's security, Gamo does not hesitate to kill his accomplice, Chou, without any sign of remorse. This act solidifies his separation from the D-Agency operatives and confirms his unwavering adherence to the Wind Agency's lethal code. According to commentary on the source material, Gamo is also noted to have been one of the first graduates of the D-Agency in the novel, adding a layer of depth to his history as a spy.