Tom Sawyer is a young boy growing up along the Mississippi River in the mid 1800s. Along with his best friend Huckleberry Finn, he spends his days ditching school, fishing, climbing trees and having adventures.

Joe Yabuki is a troubled youth, whose only solution to problems is throwing punches at them. What he lacks in manners and discipline, he makes up for with his self-taught fighting skills. One day, while wandering the slums of Doya, Joe gets into a fight with the local gang. Although greatly outnumbered, he effortlessly defeats them, drawing the attention of Danpei Tange—a former boxing coach turned alcoholic. Seeing his potential, he offers to train Joe into Japan's greatest boxer. At first, Joe dismisses Danpei as a hopeless drunk; but after the trainer saves his life, he agrees to live with him and learn the art of boxing. Unfortunately, Joe's personality makes him an unruly student, and he often falls back to his old ways. To survive the harsh world of his new career, Joe needs to trust his mentor and master the techniques taught to him. However, the road to becoming a professional boxer is rife with struggles that will test his mettle to the end.