JD (Junk Dog), a young man without an ID card, participates in underground boxing matches. With no other choice, he uses his only talent as a means to earn money in fixed matches under the guidance of his coach, Nanbu, but he thirsts to compete against real professionals on a legal basis. Luckily for him, an unprecedented event called "Megalo Box" is about to take place in the nearest metropolis, gathering the best of the best in its arena, driven by the desire to earn the title of the "strongest." Of course, our hero wants to get there at all costs, to prove to himself what his life is really worth.
The fate of the young boxer is determined by a chance meeting with Yuri and Yukiko, who happens to be the organizers of the city boxing tournament that JD has been dreaming of. The young boy, who appears reckless in the eyes of the renowned boxer who has never known defeat, deliberately challenges him and gets his attention. By sacrificing his coach, he obtains citizenship and a new name - Joe. Now he has to reach the top or die, because tomorrow's Joe has put everything at stake.