Yukiteru Amano, who goes by "Yuki," is a loner who doesn't really talk to other people. Instead, he likes to write in a diary on his cell phone. His only friend is an imaginary one named Deus Ex Machina, the God of Time and Space, whom he talks to in his head. But Yuki soon finds out that Deus is real and not just something he made up when Deus puts him in a battle royale with eleven other people. In this "Diary Game," the contestants are given special diaries that can tell the future. Each diary has its own features, which can be both good and bad.