Danpei Tange is a former professional boxer whose own ring career was cut short after he lost the use of one eye in an accident just before his first championship match. This tragic turn of events led him to a life as a trainer, but his overly aggressive and demanding methods drove his students away, causing him to be expelled from the boxing world and descend into unemployment and alcoholism, living without hope. His physical appearance is distinctive and memorable, marked by a bald head, an eyepatch covering his damaged eye, a bowler hat, and prominent buck teeth.

He is a man of stark contrasts. In daily life, he is serious, cautious, and responsible, but he has a great fondness for sake, which makes him overly cheerful and boisterous when drunk. He also displays a great deal of politeness and deference to those of a higher social standing, a trait that often irritates his protégé, who scoffs at such formalities. Despite his gruff and hot-tempered exterior, he is deeply sentimental and prone to tears, often crying out of frustration, joy, or sorrow for his boxer.

His entire existence changes upon meeting the wild and unruly street brawler Joe Yabuki. Recognizing Joe's raw, beast-like talent as the potential to fulfill his own unrealized dream, Danpei becomes possessed by a new purpose. For him, Joe represents tomorrow the hope and future he had long since lost. To dedicate himself to training Joe, he quits drinking, takes on grueling manual labor to build a small gym under the Bridge of Tears, and lives with the boy in a shabby shack. While his initial motivations are partially selfish, as he saw Joe as a means to finally produce a champion, his feelings evolve into a genuine, paternal love and unwavering devotion.

Within the story, Danpei serves as the catalyst and anchor for Joe's entire boxing career. After Joe is sent to a juvenile detention center, Danpei cannot visit him but sends letters containing boxing instructions, famously ending them with the words for tomorrow to keep Joe's spirit alive. He secures a position as a coach at the detention center to continue Joe's training, even using a weak inmate named Aoyama to teach Joe the importance of defensive skills. After Joe is released, Danpei establishes the Tange Gym, fighting to regain his license and working tirelessly as Joe's trainer and second. He is often seen clashing with Joe over strategy, as Joe prefers an instinctual, no-guard style while Danpei emphasizes careful observation and defense.

His key relationship is, of course, with Joe, whom he treats more like a stubborn son than a student. He also has a significant connection with Yoko Shiraki, the wealthy heiress who helps him gain access to the detention center and later becomes a crucial figure in the boxing world. As a trainer, Danpei's abilities are considerable. Despite his age and the damage from his past, he possesses a wild sense for the flow of a match and is always the first to notice subtle dangers, such as Joe developing punch-drunk syndrome. His own physical prowess remains formidable; even as an old, retired drunk, he can hold his own and knock down active boxers in sparring sessions, demonstrating the skill that once made him a champion contender. He is a man who gave up everything his dignity, his health, and his peace for the dream of a tomorrow that he invests entirely in his young charge.