Tetsuo Ichinomiya, nicknamed Tetsu, is a former boxer whose promising athletic career ended abruptly despite his exceptional talent. Now living as a high school dropout and self-proclaimed NEET, he fills his days gambling recklessly on dice games, pachinko, and horse races, frequently wagering substantial amounts despite the risks. Yet his streetwise survival hinges on maintained ties with both law enforcement and shadowy underworld networks—connections he strategically exploits during investigative work.

Renowned for his raw physical strength, Tetsu reportedly remains undefeated in hand-to-hand combat, a reputation solidified by rumors that even Sōichirō Hinamura, leader of the formidable Hirasaka Group, failed to best him. He extracts critical intelligence through a web of police informants and criminal associates, skillfully coaxing secrets from loose conversations over drinks. Paradoxically, his cryptic handwritten notes, likened to indecipherable hieroglyphs, often obscure the very information he gathers.

In the NEET Detective Team, Tetsu adopts a gruff mentor role, shielding younger members like Narumi Fujishima while navigating cases with pragmatic, street-smart tactics. His past as a dropout and rising athlete starkly contrasts his present reliance on informal alliances, yet this duality enables him to operate as a linchpin between the team and external factions, blending brute force with shrewd opportunism to bridge disparate worlds.