Joe Yabuki is the protagonist of Ashita no Joe 2, a former street delinquent who has channeled his immense fighting spirit into a professional boxing career. He is an orphan who spent his early life moving between facilities and living on the streets, an experience that forged his tough, solitary, and fiercely independent nature. He is easily recognized by his long, unkempt bangs, his worn beige coat, and his signature red flat cap.

At the start of the second series, Joe is a deeply altered and broken figure. The tragic death of his close friend and greatest rival, Toru Rikiishi, in the ring has left him paralyzed by guilt and grief. He has retired from boxing and wanders aimlessly, suffering from a psychological block that makes him unable to throw punches to an opponent's head, the blow that led to Rikiishi's death. This descent into despair is a direct continuation of the events of the first series, and Joe is lost, with no hope or direction.

His core motivation throughout the series is intrinsically linked to boxing. While he initially used the sport as an outlet for his raw aggression under the guidance of his coach, Danpei Tange, it ultimately becomes his sole reason for living. He describes his purpose not as winning titles, but as burning so brightly in the ring that his life is reduced to nothing but "pure white ash". This philosophy drives him to seek out increasingly powerful opponents, such as the Venezuelan Carlos Rivera, who is brought to Japan specifically to reignite Joe's killer instinct and passion for fighting. After overcoming his trauma, his ultimate goal becomes a world championship match against the invincible Mexican champion, Jose Mendoza.

In the story, Joe serves as a symbol of the lower class and its struggle to rise against a system that seeks to keep him down. His rise from the slums of Doya Town brings hope and glory to the impoverished residents there, particularly a group of orphaned children who idolize him and serve as a surrogate family. His key relationships are central to the narrative. Danpei Tange is his devoted, father-like coach who sees Joe's potential and never gives up on him. The wealthy heiress Yoko Shiraki acts as his patron; she is fascinated by his animalistic aura and helps orchestrate his path to the world stage, despite Joe harboring a deep-seated hatred for her privileged background. His deceased rival, Rikiishi, remains a constant spiritual presence, serving as the standard by which he measures all future opponents.

Joe undergoes significant development across the series. He evolves from a crude and seemingly unlikeable delinquent into a more focused, determined, and charismatic figure. His character arc is deconstructive, exploring the tragic consequences of his unwavering determination. As he climbs the ranks, he begins to develop the symptoms of punch-drunk syndrome, a form of brain damage caused by repeated head trauma, which causes his physical condition to deteriorate. Despite being fully aware of this, he continues to fight, driven by his singular purpose.

As a boxer in the bantamweight division, Joe possesses extraordinary punching power, a near-superhuman level of fortitude, and an indomitable fighting spirit that allows him to stand up from seemingly impossible knockdowns. His style is initially raw and unrefined, but he evolves into a skilled tactician. His signature techniques include the cross counter and a daring, no-guard stance where he invites attacks to create an opening for his own devastating counters. He is known for his ability to analyze and replicate his opponents' best techniques in the middle of a fight, demonstrating a high-level natural talent for the sport. His final match against Jose Mendoza showcases his ultimate transformation into a "Handicapped Badass," fighting on instinct and sheer will as his body breaks down around him.