Danpei Tange is a central figure in the story, recognizable by his unique appearance which includes a bald head, an eyepatch, a bowler hat, and a face marked by the scars of a hard life. As a former professional boxer, his own career was cut short by the loss of one eye, an injury that prevented him from achieving the championship he had pursued. Following this crushing setback, he attempted to channel his ambitions into training other fighters. However, his training methods were extremely strict, passionate, and often violent, a desperate and intense approach that his students could not endure. They abandoned him for other gyms, leaving him jobless, in debt, and ultimately exiled from the boxing world he loved, which led him to degenerate into a homeless alcoholic.

Tange's personality is a study in contrasts. In his daily life, he is serious, cautious, and responsible, but he has a notable fondness for sake. When he drinks, his demeanor shifts entirely, becoming overly cheerful and carefree, which stands in stark opposition to his usual strictness. He is also painstakingly polite when interacting with people of higher social status, a degree of formality that often irritates his protégé, Joe Yabuki, who rejects such social conventions. Despite his gruff exterior, Tange is a deeply emotional man who cries frequently throughout the story, moved by his hopes for Joe and the tragic turns their shared path takes.

Everything changes for Tange when he encounters Joe Yabuki, a wild and unruly drifter. Recognizing an immense, untamed potential in the boy, Tange makes a solemn vow to train Joe to become the best boxer in Japan, and perhaps the world. For Tange, who had been living without hope for his own future, Joe represents more than just a student; he embodies a living dream of a better "tomorrow." This is the thematic core of his character and the title of the series. To pursue this goal, he gives up his heavy drinking, as Joe has a strong aversion to alcoholism, and he only drinks on special occasions thereafter. He builds a shabby gym under the "Bridge of Tears" in the slums and works day and night doing manual labor to support Joe and their dream. Tange's motivations are not entirely selfless at first; he acknowledges a selfish desire to fulfill his own failed ambitions through Joe. However, over time, his role evolves from that of a mere trainer chasing a dream to a devoted, father-like guardian who genuinely cares for Joe's wellbeing above all else.

In the narrative, Tange serves as Joe's mentor, trainer, and surrogate father, the primary architect of his boxing career. Their relationship is volatile and defined by constant bickering, as Joe's rebellious and free-spirited nature clashes with Tange's discipline. Yet, their bond is unbreakable. When Joe is sent to juvenile detention, Tange cannot visit him directly. Instead, he sends postcards containing fundamental boxing lessons written on them—the jab, straight, and uppercut—often signed with the poignant message "for tomorrow," which keeps Joe's spirit and training alive while he is incarcerated. Later, through the wealthy Yoko Shiraki, Tange is able to enter the detention center as a coach. During this period, he employs an unorthodox method to teach Joe a crucial lesson about defense; he ignores Joe and focuses his training on the much weaker Aoyama, forcing Joe to learn how to block and move by figuring out how to beat him. This seemingly cruel act of "betrayal" is revealed to be a calculated, albeit manipulative, teaching strategy designed to make Joe a more complete fighter.

As a trainer, Tange possesses a sharp tactical mind and a keen sense of a fight's flow, even if his instructions are often ignored by the impulsive Joe. He is the first to notice the signs of punch drunkenness in Joe, demonstrating his deep understanding of the sport's dangers. Despite his age, his injured eye, and his years of hard living, Tange also retains a surprising level of physical ability. In one notable instance, he is able to fight on equal terms with Joe in a sparring session, proving that his own boxing instincts and durability remain formidable. His development throughout the story is tragic. As Joe's body begins to deteriorate from the accumulated damage of his brutal fights, Tange is forced to watch helplessly as his "tomorrow" is slowly destroyed. He keeps the gym clean, waiting for Joe's return, and his sorrow becomes a mirror to the audience's own grief, solidifying his role not just as a coach, but as a man who gave everything for another's dream, only to see it consumed by the very sport he loved.