Joe Yabuki, hardened by a tumultuous past in orphanages and facing bullies, embraces a delinquent existence in Tokyo's San'ya slum. His unruly fists pave his way until Danpei Tange, a former boxing coach, recognizes his raw talent and mentors him. Their turbulent bond evolves into a partnership caring for San'ya's homeless youth. Despite his run-ins with the law, Joe finds himself in jail, where he clashes with friends and foes, notably the skilled boxer Tooru Rikiishi. Through relentless bouts with Rikiishi, Joe transitions from brute force to finesse, earning respect and a pact for a future professional showdown. Embracing boxing as his purpose, Joe navigates Japan's boxing circuits, grappling with loss and injury, consumed by the sport's allure and the uncertainty of life beyond the ring.