Jose Mendoza is the main antagonist of the second half of the series, serving as the final and most formidable obstacle for the protagonist. He is the undisputed and undefeated Bantamweight Champion of the world, holding both the WBA and WBC belts. Hailing from Mexico, the champion is thirty years old and fights from an orthodox stance. Physically, Jose has fair skin, blue eyes, a signature mustache, and notably large, heavy hands.

His personality is defined by a quiet, calm, and unshakable confidence. He generally carries himself as a gentleman but can be direct or rude to those who are disrespectful. When he speaks, he has a deep and intimidating voice. Outside of the ring, he is a devoted family man who values time with his loved ones, which stands in stark contrast to his brutal professional persona. Within the boxing world, he is described as The Perfect Champion or The Strongest Man In The World, an aura he maintains through his flawless record and devastating power.

Jose first comes to Joe Yabuki's attention after a fight with the sixth-ranked contender, Carlos Rivera. In their match, Jose used his signature corkscrew punches to inflict severe brain damage, leaving Rivera with punch-drunk syndrome and a broken skull. Prior to this, he unified the titles by defeating the WBA champion, Harold Gomez, breaking his jaw and ultimately causing his death in the hospital. These events establish Jose as an incredibly dangerous fighter who has successfully defended his WBC title a total of seventeen times, all but one of those victories coming by way of knockout. He has killed opponents in the ring and left others with permanent, life-altering injuries.

Jose Mendoza possesses several notable abilities that make him nearly unbeatable. His signature technique is a bone-breaking corkscrew blow, a powerful twisting punch designed to inflict maximum internal damage. He also employs a technique known as the Neck Spin. Defensively, he relies on what is called The Perfect Defense, an impenetrable guard that allows him to avoid taking damage. A crucial aspect of his fighting style is that despite his immense speed, strength, and stamina, he has a notable weakness: he cannot take hits nearly as well as he can deliver them. He relies on his perfect defense to avoid being struck altogether.

Throughout his story, Jose acts as the final wall that Joe must overcome. The champion first appears as an untouchable force of nature who has systematically dismantled everyone in his path. His role is to test not just Joe's physical limits, but his very spirit. Jose believes Joe to be like a phantom due to the unbelievable number of punches he endures while continuing to fight. During their climactic fifteen-round bout, Jose is pushed beyond all previous limits. He is knocked down for the first time in his entire career and, in a moment of sheer terror, becomes desperate and commits a foul against Joe. Although he ultimately wins the match by decision, the trauma and stress of the fight leave him permanently changed. His hair turns white from the experience, and it is implied that he may have ended up punch-drunk himself, a tragic mirror of the damage he inflicted on others. This final battle breaks his spirit and prematurely ages him, tarnishing his image of the invincible, perfect champion.