Danpei Tange is a former boxer whose own ring career was cut short by the loss of one eye, an injury that forced him to abandon his personal dream of becoming a champion. Following his retirement, he channeled his ambitions into coaching, driven by a passionate and often desperate desire to train a fighter who could achieve the world title that eluded him. However, his violent and excessively strict training methods proved too intense for his pupils, who repeatedly left him for better-equipped gyms. This string of failures left him jobless, which ultimately led him to become a homeless alcoholic living in the slums.

His life took a decisive turn upon meeting a wild and wayward drifter named Joe Yabuki. Recognizing a raw, untamed talent in the boy, Danpei became convinced that Joe possessed the massive potential needed to become a great boxer. This encounter gave him a renewed sense of purpose, and he largely gave up heavy drinking, only consuming sake on special occasions due to Joe's own strong aversion to alcoholism. He vowed to dedicate himself to training Joe, hoping for a better tomorrow for both of them.

In daily life, Danpei is typically portrayed as serious, cautious, and responsible, a strict mentor who contrasts sharply with his demeanor when drunk, which is overly cheerful and uninhibited. He is also notably polite when interacting with individuals of higher social standing, a habit of formal respect that often irritates the more rebellious Joe. Throughout the story, Danpei serves as Joe's fundamental coach and father figure, guiding his career from a juvenile detention center, where he becomes the boxing instructor, to the professional ring. His key relationships include his complex, symbiotic bond with Joe, built on tough love and mutual redemption, as well as his interactions with the wealthy Shiraki family, particularly Yoko, who often provides financial support for Joe's matches.

Danpei's character undergoes significant development, moving from a broken, self-pitying drunkard living in the past to a sober and determined trainer who finds renewed hope in his protégé. While he initially sees Joe as a vessel to fulfill his own unachieved dreams, his feelings evolve into genuine care and deep personal investment in Joe's well-being and success. In terms of abilities, Danpei is a highly knowledgeable boxing strategist and trainer, despite his physical limitations from his missing eye. He is the creator of the legendary "cross-counter" technique, which becomes a signature weapon in Joe's arsenal, and he devises unique and grueling training regimens designed to bring out the best in his fighter.