Gengorō Onigawara is a character from the Inazuma Eleven anime who serves as a persistent and resourceful detective. His background is deeply tied to the original Inazuma Eleven team from forty years before the main story. Originally working as a sports reporter, he was a devoted fan of that legendary team and was profoundly inspired by their soccer. After a mysterious accident caused the team to lose a crucial match and fall into despair, Onigawara was so affected that he quit his career in journalism entirely. His singular goal became to uncover the truth behind that incident, leading him to retrain and work as a detective for decades to pursue the person he holds responsible.

Onigawara is defined by his passionate and unwavering dedication to justice, though he often displays an eccentric and intense demeanor. He becomes extremely excited upon seeing the revival of the Inazuma Eleven's techniques, such as the God Hand performed by the protagonist Endō Mamoru, feeling as though the legends have come back to life. Despite his sometimes over-the-top methods, such as ordering his subordinates to hack into networks "with their spirit," he is a competent and shrewd investigator. His primary motivation is to bring to light the crimes of the antagonist Kageyama Reiji, whom he blames for the tragedy that shattered his heroes. He feels a deep sense of resentment toward Kageyama and is determined to make him pay for the events of the past forty years.

In the narrative, Onigawara operates largely behind the scenes, providing crucial support to Raimon Junior High's soccer club. Rather than coaching or playing, his role is to investigate the various conspiracies and illegal schemes that threaten the team. He is the one who reveals the story of the original Inazuma Eleven's tragedy to Endō Mamoru, which helps convince the former coach Hibiki to return. He is frequently seen at key matches, not as a spectator, but as an investigator looking for foul play, such as when he uncovers evidence to arrest Kageyama for causing a steel frame to fall on Raimon's bench. Throughout the series, he continues his investigations into major threats, including the alien-themed Aliea Academy, where he helps protect a player's family from being used as a hostage, and the international criminal organization led by Garshield.

Onigawara's key relationships are built on his past and his mission. He was a friend of Endō Daisuke, the legendary captain of the original Inazuma Eleven, and this friendship is a core part of his motivation. He also has a long-standing acquaintance with Hibiki, another member of the original team. His relationships with the younger generation, particularly Endō Mamoru (Daisuke's grandson), are defined by his role as a supportive adult who provides information and assistance from the shadows. He also has a known connection to the Hijikata family, who help him protect a witness.

Over the course of the series, Onigawara does not undergo a dramatic personality shift, but his character is fleshed out through his persistent actions. He demonstrates significant development in his career-long pursuit of justice, from a fan who became a detective to a seasoned officer who successfully apprehends the masterminds behind the original conspiracy. After finally arresting Kageyama and later Garshield, his primary mission is effectively complete.

Regarding his abilities, Onigawara has no special soccer techniques. His notable talents lie entirely in his investigative work. He is a highly skilled detective with a network of subordinate officers and access to advanced technology, including decryption programs for hacking. He is adept at gathering evidence, conducting surveillance, and coordinating arrests. He also proves to be a capable protector, able to secure the safety of key individuals when they are threatened by antagonists.