A massive earthquake ravaged Japan's mainland and destroyed most of Tokyo, sinking three-quarters of it into the ocean.
Ten years later, the story shifts to Igarashi Ganta, a seemingly ordinary student attending Nagano Prefecture's middle school.
An escapee, a survivor of the great earthquake, Ganta has no memories of the tragedy and has lived a normal life. This all changes when a strange person covered in blood and crimson armour floats through his classroom windows. Grinning madly, the Red Man massacres Ganta's entire class but instead of killing him, embeds a red crystal shard in Ganta's chest.
Within days of the massacre, Ganta is declared the sole suspect and, following a quick trial, is sentenced to life imprisonment in Deadman Wonderland, a massive theme park like prison.