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Future Diary Redial was first announced when it was revealed in an advertisement in 2012, where it was stated that a new Future Diary manga volume, alongside with an original anime DVD with a running time for about 25 minutes long, would be released in Japan.
In early April 2013, the first chapter of Redial was released.
Redial covers the events in the Third World leading up to—and then slightly past—the final scene of the series. It follows the Yuno of the Third World. Thanks to the actions of Yuki in the series, Yuno is a far more stable and happy person than her First World counterpart. For all intents and purposes, she is a normal 14-year-old. Despite this, she is haunted by images, feelings, and moments of déjà vu that make her feel like something very important is missing in her life.
The first half of the OVA is used to show what has become of the diary holders in the Third World where the future diary death game never took place. These are generally short, comedic scenes that take place as Yuno and her classmates—the non-diary holder supporting cast of the series—take a school trip to the beach. These scenes do little to add to or take away from the series and are just there for laughs. However, occasionally we get to see something involving Yuno, hinting at the inner turmoil that is taking hold of her—like that she keeps a phone diary that is nothing but time stamps at 10-minute intervals.
The second half focuses almost exclusively on Yuno—as midnight of July 28th approaches and she begins to converse with a voice inside her head about the upcoming end of the world and the person she can't remember
She ends up going to Deus's realm, where third world Murmur tries to stop her, but is foiled by Ninth. Akise talks to her and tells her that another her murdered a lot of people and was selfish towards the one she loved. She is also able to get past him, and meets the Murmur of the First World, who tearfully gives her the First Yuno's memories. Due to his, the First Yuno is revived and transferred into the body of the Third Yuno.
Shortly after, we are shown Yuuki, who for 10,000 years, has only mourned the death of Yuno. Finally, his future diary begins to rewrite itself saying that, "Yuno came to visit." After he reads this, Yuno breaks through the walls separating the two worlds, and jumps into an ecstatic Yuuki's arms. It is here that she asks him to go stargazing with her like they had promised.
Yuno's ever-nearing breakdown is the most interesting facet of this OVA episode. Despite her much happier Third World upbringing, the knowledge that the most important person in her life is out there, yet she is unable to meet him, pushes her ever closer to the Yandere personality of her First World counterpart. It is both thrilling and heartbreaking to watch. In the final part of the OVA, it is heartwarming to see Yuuki and Yuno be reunited. Seeing Yuuki's face in absolute disbelief that his lover is still alive is a scene that can never be replaced.
And for those who need a bit more action, there is also a fun Dragon Ball Z-style fight between the still god-powered Minene from the Second World and giant mecha Murmur.3
Redial comes to a close with a short extra scene that reverts to the ending of the anime. And while this final scene may only continue a few dozen seconds beyond the end of the series proper, these closing moments give the series the feeling of completion it has been missing since it first aired over a year ago.
In the end, The Future Diary: Redial is part fan service (aka, seeing the fates of all your favorite characters) and part character development for the new Yuno—with a conclusion that gives a much more satisfying ending than that of the series. So while it's mostly an entertaining afterthought, if you enjoyed the series, you owe it to yourself to watch The Future Diary: Redial.
The Future Diary: Redial was released on DVD on July 30, 2013, in Japan. There is currently no word on an international release.