Future Diary is chapter 1 of the Future Diary manga.
The chapter starts with Yukiteru Amano in his bedroom, having just woken from his sleep. He checks his cellphone to see today's date and events that have not yet occurred, but written. Yuki brushes off his puzzlement and throws a dart at the dartboard, stating that part of his daily routine is through the accuracy of his darts. His dart hits it bulls-eye as his phone has foretold.
Later, Yuki learns about a nearby serial murderer via television and is astonished to realize that the data on his phone has predicted this beforehand. Convinced that it's just a coincidence, Yuki heads to school and several events already stated on the phone later became true.
Afterward, Yuki encounters Deus Ex Machina, the god of time and space, in his imagination who informs him that his phone is a diary that tells the future. He explains that if the phone is destroyed, so is the holder's future, meaning he or she will die.
Yuki soon the learns more about his phone. It will record everything from the coming ninety days; when a day is passed, it will be replaced by the next day's future.
Yuki later utilizes his phone in order to get top marks in his class, which irritates other students. He uses his phone in order to evade their upcoming ambush. Yuki becomes delighted with the use and efficiency of his phone. He then notices Yuno Gasai, the school's idol, looking at him. Afterward, he realizes that Yuno has made a clay model of Muru Muru, the subordinate of Deus Ex Machina.
Suddenly, his phone foretells that Yuki is going to be chased by the serial killer and murdered and a "Dead End" is noted. Yuki begins to panic, and Yuno appears behind him, asserting that that is his future. Frightened, he escapes from the classroom and notices that his future has changed. Initially, Yuki believed that he managed to evade her, but she outmaneuvers him.
Yuki enters a building and climbs into the elevator. However, Yuno reaches him and it dawns to Yuki that she is another future diary holder. However, Yuno reaches him and it dawns to Yuki that she is another future diary holder. Convinced that she will kill him, he considers stabbing her with his dart that he has concealed in his bag. Abruptly, Yuno kisses him and she tells him that he did not stab her and declares that as the future.
She then points out the serial killer from below and recognizes him as the third future diary holder. She explains that she knew the serial killer is pursuing Yuki because of her diary holder. Yuno says that her diary is the Yukiteru Diary where it will show Yuki's future in every ten minutes. Shocked, he sees her as an extreme stalker. Yuno then changes the direction of the elevator to the 17th floor instead of the 14th because that is where he is destined to be killed. She elaborates on the survival game the diary holders are participating in and how they will attempt to eliminate each other.
They arrive at the rooftop and Yuno announces that they are going to strike first before the serial killer because running away is pointless. She discloses her plan to him, which includes the usage of Yuki's dart.
Soon after, the Third reaches the rooftop as well. Meanwhile, Yuki is hiding nearby, anxious as he only has one dart which indicates only one chance. He recalls that their diaries are weapons, but they also have weaknesses because they are the futures of the holders. In other words, if he manages to destroy the Third's diary, the latter will inevitably be erased from existence.
Yuki then reveals himself and tosses the dart which penetrates the Third's diary with precision. The Third then dies. Disappointed by how simple the death was, Yuno opts that they have dinner at Yuki's house as his mother won't be back tonight.
Later, Yuki confronts Deus who tells him that he has never ascertained that only Yuki is a diary holder. Deus explains that it is the survival game for diary holders where the last one standing will become his successor. Yuno is shown behind Yuki, reassuring him that she will protect him, and he grows apprehensive.