Nagi Taira was once the world's most lethal assassin, but his life changed when he shielded his younger sister Shizuka from a hail of bullets. The incident left him in a persistent comatose state, confined to a wheelchair and unable to interact with the world. However, Nagi possesses a unique and brutal physiological condition: he can briefly regain consciousness only when he is the target of another persons murderous intent. Believing that exposure to extraordinary levels of killing intent is the key to her brothers full recovery, Shizuka does not seek a quiet cure. Instead, she straps Nagi into a heavily modified, weaponized wheelchair known as a tank chair and drags him on a violent rehabilitation journey across a decaying dystopian landscape.

The series is set on Guicheng Island, often called the most dangerous town in the universe, a lawless and cluttered urban wasteland where genetic doping is common and gangs rule through absolute violence. Shizuka works as an assassin, but she is not the killer; her role is to arrange contracts and lure formidable foes directly to her brother. When an enemy approaches with the intent to kill, Nagi snaps awake from his catatonic state, unleashing his former lethal skills from his armored chair to annihilate his target in hyper-violent confrontations.

The central narrative arc follows this siblings desperate and bloody journey as they face a rogues gallery of eccentric enemies, from snipers with prehensile mechanical eyes to monstrous fighters empowered by illegal enhancements. While the surface story is a relentless action thriller filled with graphic violence, the emotional core is the unspoken bond between Nagi and Shizuka. They rarely vocalize their feelings, but their entire existence is a mutual sacrifice as they navigate a bleak world, supported by a cast of quirky characters including Radio, Naozumi, Touko, Uzu, and Sensei. The story explores themes of love, fate, and the lengths siblings will go to for one another, blending a pop and comical visual style with a genuinely dark and desperate fight for survival.