Ganta Igarashi has been convicted of a crime that he hasn't committed, and sent to a new, privately owned and operated prison, where the inmates are the main attraction in a modern day twist to the gladiatorial coliseums of ancient times. Throw in a healthy dose of weird little girl, some new-found super powers, and a little conspiracy theory, and you have Deadman Wonderland.
In the distant future, the war between the human race and the Gamilon has taken its toll on the planet Earth. Constant bombardment of radioactive asteroids has rendered the planet's atmosphere uninhabitable. As a means of relief aid, Queen Starsha of the planet Iscandar offers the Earth Forces a device that can completely neutalize the radiation off the planet. For this task, the space battleship Yamato is launched from the remains of its World War II ancestor on a 148,000 light-year journey. However, the crew of the Yamato has only one Earth year to travel to Iscandar and back, or the human race will come to an end.
Yukiteru (Yuki) Amano is a loner who never really interacts with people and prefers writing a diary on his cell phone, with his only companion being an imaginary friend named Deus Ex Machina, the God of Time and Space. However, Yuki soon learns that Deus is not a figment of his imagination but real when Deus makes him a participant in a battle royale with eleven others. Within this "Diary Game", the contestants are given special diaries that can predict the future, with each diary having unique features that gives it both advantages and disadvantages.