A decade before the story begins, a meteorite strike devastates central Tokyo. In the aftermath, the megacity is split into two distinct zones: a prosperous sector reserved for the wealthy and a lawless, destitute slum built around the meteor crater. It is in this slum that Riku Kurita, a resolute 13-year-old boy orphaned by the disaster, lives with his surrogate uncle, a middle-aged police officer named Goro Fujimoto.

Despite the harsh environment, Riku survives by relying on his wits and the kindness of Fujimoto. However, this fragile peace is shattered when Fujimoto is assassinated while preparing to expose the extensive criminal activities and corruption of Eishu Kidoin, the powerful Inspector General of the Tokyo police. Riku is the sole witness to the murder, but instead of justice, he is framed for the crime by Kidoin himself. With no recourse, Riku is arrested and sent to the Paradise Island Penitentiary, a harsh maximum-security prison isolated from the mainland.

The central narrative follows Riku's fight for survival within this brutal system. At Paradise Island, he is surrounded by hardened gangsters and violent criminals who quickly target him as a weakling. Driven by his burning rage and a desperate desire to avenge his uncle by revealing the truth about Kidoin, Riku refuses to be broken. He begins to form alliances with other inmates and devises a plan not just to survive, but to escape. A key part of his education involves learning unconventional skills from fellow prisoners, such as Ichiro Tanaka, a revolutionary who can remove his handcuffs at will and teaches Riku how to become invisible to the guards.

After much struggle, Riku and his companions successfully break out of Paradise Island. Their freedom is short-lived, as they fall directly into a trap set by Kidoin. Instead of being returned to a regular prison, they are sent to a secret, illegal facility known as Hell Island. On Hell Island, prisoners are forced into brutal labor, digging massive underground mines on the surface while opium is cultivated and manufactured above ground. The conditions are a death sentence, with most inmates dying within a month. Riku and his friends must rally their strength once more to survive this new circle of hell and attempt another daring escape.

The main antagonist is Eishu Kidoin, who serves as the story's primary villain. He is a chillingly manipulative sociopath who uses his authority to eliminate any obstacle, treating people as disposable tools. He possesses terrifying insight into human psychology and takes a perverse pleasure in explaining his machinations to his victims. A spin-off manga, Boss Renoma: Shujin Riku Gaiden, focuses on the backstory of Sasaki Renoma, a powerful gang boss from the slums who becomes a key ally to Riku.