"Garouden Boy" centers on Tamon Yamashita, a high school student with a natural talent for martial arts. Despite his skills, Tamon is reluctant to fight, preferring a peaceful life. However, his life takes a dramatic turn when he encounters the underground fighting world. After being coerced into participating in an illegal fighting tournament, Tamon discovers his latent potential and begins to embrace his abilities. The series explores his journey as he navigates the brutal and often dangerous world of underground combat, facing off against formidable opponents who push him to his limits.

The narrative delves into Tamon's growth as a fighter and his struggle to reconcile his pacifist nature with the violent reality of the fighting circuit. Along the way, he encounters a diverse cast of characters, each with their own motivations and fighting styles. These include mentors who guide him, rivals who challenge him, and allies who support him. The story also examines the psychological and physical toll of combat, as Tamon grapples with the moral implications of his actions and the consequences of his choices.

As the series progresses, Tamon's skills evolve, and he gains recognition within the underground fighting community. The stakes escalate as he faces increasingly powerful adversaries, culminating in high-stakes battles that test his resolve and abilities. The manga balances intense fight sequences with character development, providing insight into the backgrounds and motivations of both Tamon and his opponents. Themes of perseverance, self-discovery, and the pursuit of strength are woven throughout the narrative, creating a compelling exploration of martial arts and personal growth.