The reclusive middle school student Yukiteru Amano finds himself whisked into a fierce game of survival by the god of space and time, Deus Ex Machina, in which the victor shall inherit Deus' unlimited power. All 12 contestants, including Amano, are composed of people who regularly keep diaries, but there is a twist: each person's diary has been turned into a "Future Diary," making it capable of telling the future to various degrees.

Amano possesses a "Random Diary" on his cellphone, which gives him accurate descriptions of his surroundings. He is reluctant to fight but his desperation to survive leads to him teaming up with fellow classmate and diary holder Yuno Gasai, an attractive girl who has a strange obsession with Amano.

But as this bloody battle royale plays out, shocking revelations are brought to light, changing the very nature of this twisted game.