Yukiteru Amano is a timid middle‑school student who habitually records every moment of his day on his smartphone—a digital journal. Though he has no friends at school, he is often seen chatting with what appear to be imaginary companions: Deus Ex Machina, the god of time and space, and his attendant Mur Mur.
One morning, Yukiteru notices that some of the events he will experience are already shown on his phone. At first he dismisses it as a fluke, but gradually he realizes that the entries actually predict what will happen soon. After using this strange advantage for a day, he discovers that his classmate Yuno Gasai keeps a similar log.
When the two join forces to confront an odd pursuer and return home, Deus Ex Machina reveals that they—together with ten other participants—have been pulled into a survival contest whose champion will inherit the deity"s throne. With no other choice, Yukiteru and Yuno must rely on their "Future Diaries" to endure this brutal battle royale.