Genta Doi is introduced as a classmate of Haruo Yaguchi and Akira Oono during their elementary school years. From a young age, he becomes captivated by Akira, admiring her beauty, intelligence, and wealthy family background. This admiration quickly turns into an obsession, and he repeatedly attempts to win her affection or propose an engagement, facing consistent and often blunt rejections each time.

Physically, Genta is considered handsome, though his looks are frequently undermined by his personality. A notable visual motif accompanies him, a shimmering, star-like aura that often sparkles around him, emphasizing his self-perceived princely persona, although this effect is typically undercut by his subsequent awkward or comical behavior. His personality is a study in contradictions: he projects a flamboyant, grandiose, and supremely confident image, yet he is persistently insecure and socially awkward. He tends to be presumptuous and overly theatrical, believing himself to be far more popular and charismatic than he actually is. His efforts to appear cool or sophisticated are often ill-judged and backfire, making him come across as irritating rather than impressive to those around him.

Motivated primarily by a desire for recognition and romantic success, Genta’s goals are a source of continuous comedic misfortune. His fixation on Akira leads him to organize events meant to bring them closer, most notably a disastrous amusement park group outing. This plan fails largely because he misunderstands Akira’s interests entirely, and it culminates in a deeply embarrassing incident with another student, Chihiro Onizuka, inside a Ferris wheel. Witnessing the natural, game-focused connection between Akira and Haruo fuels intense jealousy and disdain within him, and he frequently tries to belittle Haruo to assert his own perceived superiority. Despite his rivalry with Haruo, he, along with another former classmate named Kotaro Miyao, forms a loose social trio with him, becoming a recurring part of the group dynamic even as he continues to mock them both. Genta’s friendship with Miyao proves to be his most stable and consistent relationship, enduring from high school into their adulthood.

Genta’s role in the story is largely that of a comic foil. He provides levity through his grand but failed gestures and his obliviousness to his own social standing. He does, however, have a faint, accidental connection to the world of gaming that defines the series. While not a dedicated player like Haruo, he exhibits a bizarre and inexplicable talent for luck-based arcade games. On two separate occasions, he accidentally hits a 999-times multiplier jackpot on a medal game, leaving himself and everyone else utterly bewildered by his sudden fortune.

Over the course of the series, Genta shows minimal character development in terms of social success or romantic achievement. He continues his fruitless pursuit of popularity and girlfriends through high school without any more success than in elementary school. In adulthood, as depicted in the spin-off Hi Score Girl DASH, Genta becomes a physical education teacher at his former junior high school. He retains his flashy demeanor and the sparkling star effect, and he works alongside Koharu Hidaka, who has also become a teacher. His personal life remains stagnant; he stays single and has never had a girlfriend. This is comically highlighted during a drinking outing with Miyao, where he embarrassingly confesses to still being a virgin. His character thus represents a consistent pattern of earnest yet misguided attempts for recognition, ending as a lovable, eternal outsider.