Sign Up (サインアップ, Sain Appu) is the first episode of the Future Diary anime series.
The scene opened in a middle of a room where a girl, crying, waking up someone who seems to be dead. The scene fades and switches into a dark room with a girl talking to her parents when suddenly a mysterious person stabs her to death. But before losing her breath, she requests for help from Amano Yukiteru in a faint voice.
The scene changes to a young boy named Yukiteru "Yuki" Amano, a loner who spends his time writing in his cell phone diary. Going home from school he immediately remove his shoes and brush up to his room to talk to his imaginary friend, Deus Ex Machina, God of Time and Space.
While talking to his "friend" Muru Muru, an assistance of Deus talks to Yuki about his No Difference diary saying that it is a diary with no purpose. Deus ask him if he's feeling lonely he answered back that he is "not really" lonely. Deus ask again if "what if he could change the situation", what would he do. Yuki, clueless of what Deus is talking about, hands Yuki's cell phone back then asks Deus about what is he scheming with the God replying that he is planning an "interesting game", with Yuki not minding what Deus said, thinking that he is only an imaginary friend.However, one morning, he finds his diary entry for the day has been filled in already. Strange yet, the events portrayed in the diary start coming true. Deus, who reveals he is an actual God, warns Yukiteru that if he loses his diary that he will die. Yukiteru later uses his diary to his advantage by evading bullies and cheating on a test. Later that day, Yukiteru saw a Dead End flag raised in his phone. After that, he is approached by a stalker named Yuno Gasai who also possesses a Future Diary cell phone. Instead of staying still he got scared and ran away from Yuno but the girl chases him and until he gets inside a nearby building which is under construction. Yuki quickly enters an elevator clicking the 14th button. Before the elevator set to go up, Yuno enters the door. A shocked Yukiteru who is confused about what's happening was pinned by Yuno in the elevator wall and kisses him. She then changes the floor they were supposed to stop, changing it to stop at the top floor. Reaching the roof, Yuno formed a plan. Helping him evade Takao Hiyama, the killer and 3rd diary owner, Yuno enables Yukiteru to throw a dart at the killer's phone, which causes him to vanish into a vortex.
Afterwards, Deus explains the rules of the survival game to Yukiteru and the remaining diary owners in which they must try to kill each other in order to win the right to succeed him.
- During the end of the episode, Yuno's infamous "Yandere trance" was so popular that it was turned into an internet meme, with internet users editing Yuno's face to look like other characters from numerous series.