Yukiteru Amano is a timid middle school student who habitually records his daily activities on his phone, maintaining a digital diary. Although he has no friends at school, Yukiteru is often observed conversing with his purportedly imaginary companions: Deus Ex Machina, the god of time and space, and Deus' servant, Mur Mur. One day, Yukiteru wakes to find that specific events of his day are displayed on his cellphone in advance. While he initially dismisses this as a coincidence, he gradually realizes that the incidents written in his phone actually occur in the near future. After spending the day taking advantage of this new asset, Yukiteru discovers that his classmate Yuno Gasai possesses a similar diary. As the two join forces to defeat a strange pursuer and return to their respective homes, Deus Ex Machina explains that they—along with 10 other contestants—have been drawn into a survival game whose winner will become the deity's successor. With no other options, Yukiteru and Yuno must use their cellphones—now called "Future Diaries"—to survive this unforgiving battle royale.