Set in a city where the wealthy are licensed citizens and those on the outskirts are unlicensed citizens living in poverty, the sport of megalo boxing has risen. Megalo boxing is a popular sport where the boxers fight while wearing a metal frame -- something that makes their attacks even more lethal. Junk Dog fights in the underground illegal rings with fixed fights overseen by his coach Gansaku Nanbu. After he almost crashes his motorcycle into Yukiko Shirato, her bodyguard challenges Junk Dog to fight him in Megalonia -- something reserved for licensed citizens. Junk Dog now works to prove himself the best fighter and move up the ranks in order to attend Megalonia.