Junk Dog, later known as Gearless Joe and eventually Nomad, is the central figure of his narrative, a man whose very identity is defined by his life in the ring. He begins with no name to call his own, only the moniker Junk Dog, a fitting label for an underground Megalo Boxer forced to throw fights in a fixed-match circuit under the crooked management of Gansaku Nanbu. Living in the gritty, impoverished outskirts of a futuristic city, his existence is one of survival and simmering frustration, as he is denied the one thing he craves: a genuine, all-out fight. This dissatisfaction with a life of staged defeats defines his initial state, a caged animal longing for a real challenge.

His entire trajectory changes after a chance encounter with Yuri, the undefeated champion of Megalonia, the most prestigious Megalo Boxing tournament. After being effortlessly knocked out by Yuri, Junk Dog becomes possessed by a singular, burning motivation: to face the champion again on the grand stage and defeat him. This goal drives him to shed his former identity and fight his way into the professional ranks. In his first official match, he creates a new persona by discarding his worn-out exoskeleton gear, entering the ring with nothing but his own body and fists. This shocking act earns him the famous nickname Gearless Joe.

As Gearless Joe, his personality comes into sharp focus. He is, on the surface, a laid-back and easygoing individual, rarely showing anger outside of the ring. However, once the match begins, he transforms into a fierce and determined competitor. He is a Blood Knight at heart, fighting not for fame or money, but for the pure thrill of testing his limits against a strong opponent. His philosophy of boxing is one of honesty and full effort; he disdains holding back or using deceptive tactics, preferring to face his opponents head-on with everything he has. This hot-blooded spirit is balanced by a natural talent for reading opponents, making him a skilled counter-puncher who often wins by landing a single, decisive blow after withstanding his enemy's assault. He is a true Determinator, possessing an almost superhuman willpower that allows him to take incredible amounts of punishment and keep getting up, refusing to ever give up on a fight.

His role in the story is that of the ultimate underdog who challenges a corrupt and technologically dominated system. He is a man with no legal identity or citizenship, an illegal fighter who crashes the grand tournament to prove that raw human spirit and will can overcome any obstacle, including advanced mechanical gear. His key relationships are central to his journey. His bond with his coach, Nanbu, is complicated, starting as a dishonest business partnership based on throwing matches. It evolves into a genuine yet fraught mentor-student relationship, with Nanbu eventually sacrificing his own eyesight to give Joe a chance to win freely. He also forms a family-like bond with Sachio, a young pickpocket who becomes Nanbu's assistant and Joe's de facto younger brother. His rivalry with Yuri, the stoic and powerful champion, is the story's core, moving from mutual respect to a final, gearless brawl that redefines the sport itself.

Joe undergoes a profound development across the narrative. In the first part, he ascends from a nameless junk dog to the champion of Megalonia, proving his worth to the world. The sequel, Megalobox 2: Nomad, finds him years later, having vacated his title and fallen into a deep depression. Now calling himself Nomad, he is a broken man, addicted to painkillers and living as a drifter, fighting in the underground again while trying to escape the guilt of past sins, specifically his perceived abandonment of Nanbu and Sachio. His development in this chapter is one of redemption, as he slowly confronts his self-destructive behavior, which borders on a death wish, and finds a new reason to live by helping others, including a refugee boxer named Chief. His arc moves from seeking glory to finding peace and atonement.

In terms of notable abilities, Joe is a remarkable physical specimen. He is a Badass Normal, fighting and defeating opponents who use powered exoskeleton gear using only his natural strength, speed, and resilience. His combat style is aggressive and instinctual, relying on relentless pressure and devastating counter-punches. He has a high threshold for pain, and his body is covered in scars from countless brutal battles, including a distinctive J-shaped scar on his cheek from his first encounter with Yuri. Physically, he is tall and muscular with dark, tanned skin and black hair, often seen wearing a distinctive green military jacket. Despite his world-weary appearance, especially in the second season where he sports a beard of sorrow, his core physical prowess and unyielding fighting spirit remain his most defining attributes.