Fuyuo Shigaraki is flat broke, divorced, and barely scraping by. With his daughter in desperate need of 3 million yen, this middle-aged underdog is at the end of his rope. That’s when he meets a bizarre self-proclaimed “high school girl brawler” who gives him an outrageous idea. "Hey, Mister… why not make money with street fights?" Dragged into the underground world of cash brawls, Fuyuo reluctantly steps into the ring — until the first punch lands. Turns out, this average old man isn’t so average after all. He’s the only man to ever draw against the reigning MMA world champion. As fists fly and reputations crumble, the beast he buried long ago awakens once more — and a new legend of the streets is born.