Cut from there to school. Yukiteru Amano, our MC calls himself an observer. He doesn't participate in things, but obsessively keeps track of everything that happens on a diary in his cell phone.
He has no real friends, but rather, imaginary ones.
Hinata is Tenth's daughter and has his diary. She takes Amano's diary at knifepoint.
Aru Akise, another classmate, fakes having a diary and engages Hinata in a high stakes bet. Can he beat future information? Yes. Lying to Amano puts false information in the diary.
Fourth comes for them, but Ninth arranges things so the other cops see what he's up to and arrest him. His diary shows what happens on his cases, so it's useless now.
He asks Ninth for one final favor, and pays with his life, destroying his own diary.
The people who have actually come are not Child Diary users, but Seventh: Ai and Mar are lovers whose paired Love Diaries tell them how to protect each other. (They are both Seventh.)
They see this as a lover's duel: which couple's love is strongest?
The bank Eleventh is in was owned by Gasai's parents. The vault has a retinal scanner that will only open for Eleventh, Gasai's parents, and the real Gasai Yuno.
Nonetheless, she is able to open it and kill Eleventh.
Bad news: Deus Ex Machina is a load-bearing God. As he reaches the end of his life, reality starts to break down.
Akise breaches the gates of heaven to confront Deus. But Deus says that he isn't even real - he's an Observation Terminal for Deus to keep tabs on the diary keepers.
Unable to beat Akise's diary, Gasai injuries herself, leaving Akise in a position where he has to save her, because if he let's her die, Amano will never trust him again.
Meanwhile, Amano's friends give him the bad news: even with the power of God, resurrection isn't possible.
Amano refuses to believe, killing his way through them to get to eighth.
Akise fights Gasai, crushing her diary, but she doesn't die. Why not? A mortally injured Akise tries to put the pieces together. Finally, he realizes what's going on and limps forward to tell Amano.
You can't bring back the dead, but there's more than one way to skin a cat.
(Those who have seen _The Visitors_ know.)
Gasai Yuno has already won the game and become God. When she was unable to resurrect Amano, she travelled through time, killed herself and took her own place.
God Gasai confronts her younger self. But the younger Gasai is still innocent, and hopes that her mother will recover from her depression. She has not yet given in to despair.
God Gasai hesitates just long enough for young Gasai's parents to arrive and protect her.
Amano rejects the false world and breaks free to confront Gasai. He tells her to kill him so she can be the God of the second world. But she can't do it and kills herself instead, leaving Amano the winner.
On called simply _The Future Diary OVA_ predates the series and is basically a <we should totally have an anime> proposal covering a few scenes from the first few episodes. Nothing noteworthy.
The Third World Gasai is having déjà vu and memories that don't make sense.
She goes on a quest to the spirit realm and retrieves the fragment of Second World Gasai's memories, then breaks through the dimensional barrier to be with Amano again.
I really enjoyed it. The stakes started high and just for higher. They ratcheted up the tension without ever breaking suspension of disbelief, even when we got to the time travel and godly powers level.
So, let's get serious: despite having Amano as the alleged narrator, this is really Gasai's show.
We as the audience are left asking, <what's up with her?> It's not immediately clear if she's crazy in a real way, or just in whatever way is convenient for the plot.
But in the end, it all makes sense, and that's great.
People praise _Bakemonogatari_ for its interrogation of the Tsundere stereotype and what it would take to make a person behave like that. _The Future Diary_ does something similar for the Yandere.
Unable to beat Akise's diary, Gasai injuries herself, leaving Akise in a position where he has to save her, because if he let's her die, Amano will never trust him again.
Meanwhile, Amano's friends give him the bad news: even with the power of God, resurrection isn't possible.