Future Diary is a rollercoaster psychological thriller anime series with plenty of twists. It ran from 2011 to 2012 with 26 episodes and a lot happens. The main protagonist, Yukiteru, and eleven other people all became part of a survival game where the losers die and the winner becomes the new god in order to avoid the apocalypse. Yukiteru is quite weak and a bit of a coward, so he teams up with his female classmate, Yuno, who is incredibly talented and strong but has psychopathic tendencies and is obsessed with him.
By the end of the story, enough twists happen that the series is worth watching more than once. The biggest turning point is when Aru Akise reveals Yuno's big secret to Yukiteru. He reveals that the Yuno everyone has been interacting with is actually a Yuno from another timeline, a Yuno that won the survival game and became a god.
The Truth About Yuno And Muru Muru
The Yuno known to the audience is from another timeline, one where she won the survival game and became a god. However, how she became a god was a bit of an accident. In her original world, she and Yukitersu were the only remaining contestants and loved each other enough not to kill each other for the god title. They decided to commit a double suicide and let the apocalypse happen.
Yuno, however, decided she had a different plan. She thought that with the power of a god, she could bring Yukiteru back to life. So she did not swallow the pills for the planned suicide and only Yukiteru died. However, when she became god she found out that he could not bring the dead back to life. Muru Muru, Deus' assistant that then became Yuno's, suggested Yuno instead could travel to a different timeline instead to be with another Yukiteru. Yuno then proceeded to travel to the timeline the audience knows and killed the Yuno from that timeline and replaced her. Muru Muru also replaced her second-world self by imprisoning the original. Muru Muru of the first is considered the real antagonist of the series. She wishes to dethrone Deus and also hopes to steal godhood from Yuno. By the end of the story, though, her plans are destroyed.
The Third World, Explained
After Aru Akise shows Yukiteru the truth about Yuno, that she already won the survival game in the first timeline, Yukiteru confronts her about it. This ruins her plans to relive her time with Yukiteru, and she decides to go to a third timeline to start a survival game all over again. Yukiteru is able to follow her with the help of Nine, as Nine gets gifted with some god powers from Deus since he was suspicious of Muru Muru helping Yuno.
Yukiteru does everything to protect the third world's Yuno. The first world Yuno, however, imprisons Yukiteru in an illusion world and attempts to kill her third timeline self. She tells this other her about the horrid fate that awaits her, like her abusive parents locking her in a cage.
However, the third timeline Yuno reacts with optimism, believing things will work out. This is major for the first timeline Yuno, as she realizes how different she has become. When she strikes at third timeline Yuno, her parents protect her. This means the timeline is already seeming more hopeful than others. There is hope for the Yuno of the third timeline to have a happier life.
Yukiteru manages to break out of the illusion world with the second Muru Muru. The second Muru Muru defeats the first world Muru Muru and Yukiteru asks Yuno to kill him to become god again in the second world. However, Yuno instead kills herself and Yukiteru becomes the new god.
Yukiteru As God
Yukiteru becomes the new god but is devastated by the loss of the first timeline Yuno he knew and loved. Just like she with him in the first timeline, he could not bring her back to life. He spends 10 thousand years sulking and looking at his diary future diary that reports Yuno's suicide. At the very end, though, the message changes to Yuno coming to visit him. The series ends there, but way later an episode was released to explain what happened.
The Yuno that visits Yukitersu is actually the third world Yuno. The first world Yuno's memories and consciousness were given to her by the first world Muru Muru, and so she sought Yukiteru out to help him with his godhood. This snaps him out of his sadness, and they begin making a new world together. It is made official by Deus of the third world that both Yukiteru and Yuno are his dual heirs. As for third world Yukiteru, that one never meets Yuno. The third timeline has them go to different schools.