Gansaku Nanbu coaches and manages an underground boxer named Junk Dog in a dystopian world where stateless populations languish in slums. Burly, tanned, and bearded, he sports a black eye patch over his right eye—forfeited in a debt settlement—and dons a pale cap, yellow shirt, and orange vest in his early appearances. His survival hinges on orchestrating rigged bouts for his protégé to pay off dog-racing gambling debts.

Once a boxer and gym owner, financial ruin forced him into a nomadic life in a truck after shutting down his training facility. A former student, Tatsumi Leonard Aragaki, returned from military service to find the gym closed, breeding lasting resentment. To manage mounting debts, Nanbu partnered with mob boss Fujimaki, staging fixed fights until an unscripted victory by his protégé spiraled their obligations. Desperate, they entered a high-stakes tournament under a fabricated identity for the boxer, chasing prize money and legitimacy.

Evolving from a scheming survivor to a committed mentor, Nanbu guided his protégé’s rise through the tournament, balancing underhanded tactics with steadfast support. Diagnosed with cancer in later years, his death fractured ties with former mentees, including a group of orphans embittered by his protégé’s absence in his final moments.

His defiant declaration—“I’ll show you exactly what we frauds can do!”—mirrors his duality: a manipulator clawing beyond exploitation in a divided society. His legacy lingers in themes of sacrifice, redemption, and the scars of systemic inequality.