Shōhei Harada is a student at Meisei High School and a significant supporting character known for his large, physically imposing stature and intimidating appearance. He maintains a gruff and often aggressive outward attitude, which initially leads to him being perceived as a bully or a delinquent. In junior high, he was part of a circle known for street brawling alongside Akio Nitta, establishing a reputation as someone not to be trifled with. However, this rough exterior conceals a fundamentally kindhearted and loyal individual who demonstrates genuine concern for the wellbeing of those he considers friends. Despite his tough demeanor, he has notable vulnerabilities, such as being weak to alcohol to the point of getting drunk from a single glass of beer.

Harada's primary role in the story is that of a spiritual mentor and steadfast supporter for Tatsuya Uesugi. From early on, he is one of the few people who recognizes Tatsuya's latent potential and innate talent, even when everyone else compares Tatsuya unfavorably to his more diligent twin brother, Kazuya. When Tatsuya hesitates and ultimately gives up on joining the baseball club, it is Harada who forcefully recruits him into the boxing club. This decision proves to be a crucial turning point, as the boxing training provides Tatsuya with the physical conditioning and mental fortitude he was lacking, helping to reshape his passive and conceding personality. As a member and eventual captain of the boxing club, Harada is depicted as tremendously strong; he is skilled enough that, even with a small nail embedded in his left hand, he nearly defeats a boxer who placed third in a national tournament using only that hand.

Beyond being a physical catalyst for Tatsuya’s growth, Harada serves as a perceptive observer and commentator, often seeing situations more clearly than the main characters themselves. He accurately discerns the delicate and complex relationship dynamics between Tatsuya, Kazuya, and their childhood friend Minami Asakura, recognizing Minami's true feelings and encouraging Tatsuya to actively compete with his brother. Like many other male characters in the story, Harada harbors feelings for Minami, as evidenced by his consistent presence at her rhythmic gymnastics competitions to cheer her on. However, his affection is expressed through a selfless desire for her happiness, leading him to strongly support the relationship between Tatsuya and Minami. He has a notable history with Akio Nitta, stemming from their shared delinquent past, and is instrumental in introducing Tatsuya to him later in the story.

Throughout the narrative, Harada demonstrates significant personal development. While his intimidating presence remains constant, his role evolves from that of a secondary school brawler to a reliable advisor whose words carry great weight with both Tatsuya and the audience. He remains an unwaveringly loyal friend who supports Tatsuya after Kazuya's death and through his subsequent return to baseball. His appearances extend beyond the original story, as his continued presence is confirmed in the sequel series, MIX, where even as a fifty-year-old, he maintains his formidable physique and boxing skill.