"Deadman Wonderland" is set in a dystopian future where Japan has been devastated by a massive earthquake. The story centers around Ganta Igarashi, a seemingly ordinary high school student whose life is upended when a mysterious figure known as the Red Man massacres his entire class. Ganta is the sole survivor, but he is falsely accused of the crime and sentenced to death. He is sent to Deadman Wonderland, a privately owned prison that doubles as a twisted amusement park where inmates are forced to perform dangerous stunts for the entertainment of the public.

Within Deadman Wonderland, Ganta discovers that the prison is a place of grotesque experiments and brutal survival. He learns that he has been implanted with a Branch of Sin, a unique ability that allows him to manipulate his own blood as a weapon. This ability marks him as a "Deadman," a special class of prisoner forced to participate in deadly gladiatorial battles called Carnival Corpse. These battles are orchestrated by the prison's overseers, who seek to exploit the Deadmen's powers for their own gain.

Ganta's primary goal is to survive the harsh environment of Deadman Wonderland while uncovering the truth behind the Red Man and the conspiracy that led to his imprisonment. Along the way, he forms alliances with other Deadmen, including Shiro, a mysterious girl with a childlike demeanor and a deep connection to Ganta's past. Shiro possesses immense strength and agility, but her memories are fragmented, and her true nature remains enigmatic.

As Ganta delves deeper into the prison's secrets, he encounters a variety of adversaries, including other Deadmen with their own Branches of Sin and the corrupt officials who run Deadman Wonderland. The narrative explores themes of survival, betrayal, and the struggle for justice in a world where morality is often blurred. Ganta's journey is marked by intense battles, emotional revelations, and a growing understanding of the dark forces at play within the prison.

The series builds toward a climactic confrontation that ties together the mysteries of the Red Man, Shiro's identity, and the true purpose of Deadman Wonderland. The story is characterized by its fast-paced action, psychological tension, and a focus on the resilience of its characters in the face of overwhelming adversity.