Genta Kojima, a six-year-old member of the Detective Boys, combines a sturdy frame with a buzzcut hairstyle accentuated by a distinctive circular bald patch on his left temple. His physical prowess positions him as the group’s frontline force, frequently charging through barriers during cases. Though he loudly claims leadership of the team, his boldness and tendency to overlook risks often steer investigations into chaos. A fervent food enthusiast, he measures monetary value through his obsession with braised eel rice bowls and sometimes fumbles kanji interpretations when preoccupied by hunger or adrenaline.

Loyalty defines his core, as he consistently shields friends in peril despite his boisterous demeanor. He idolizes his father, Genji Kojima—a self-proclaimed "Child of Edo"—while his mother’s background remains unmentioned. Within the group, he playfully competes with Mitsuhiko Tsuburaya for Ayumi Yoshida’s attention, though tensions seldom rise beyond lighthearted rivalry. Despite privately recognizing Conan Edogawa’s superior deductive skills, Genta stubbornly upholds his self-declared authority during missions.

A speculated shellfish allergy (File 1039) and a name derived from "origin" and "plump" kanji subtly nod to his rotund build. Across media portrayals, he remains an unwavering comic relief figure, leveraging his strength for practical solutions and prioritizing snack-driven incentives. His narrative role steadfastly emphasizes these traits without expanded backstories or arcs in supplementary materials.