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Yukiteru Amano (or Yuki) is a loner who never really interact 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.

Mirai Nikki (literally Future Diary) is a dark manga about the asocial Yukiteru Amano, who obsessively keeps journals. One day, he finds that his imaginary friend Deus Ex Machina, the lord of time and space, has made his cell phone diary able to predict the future.

Rintaro Okabe is a self-proclaimed "mad scientist" who believes that an international scientific organization named SERN is conspiring to reshape the world according to its own interests. He and his friend Itaru Hashida inadvertently create a gadget able to send messages to the past.