Mirai Nikki is a 14 volume manga by Sakae Esuno, about a young boy called Yukiteru Amano who is a complete loner and spends most of his days writing down the details of his life into a diary on his mobile phone. Naturally, he has no friends and is teased constantly by his classmates. However, he does have two friends in his imagination: the god of space and time, Deus Ex Machina, and his little demon assistant, Murmur. Deus Ex Machina comes up with a game one day that could change his life forever. He takes Yukiteru's phone and makes it so his diary gives him little memos of the future ahead, the Random Occurences Diary.
At first, Yukiteru uses it for the mundane things we all would. He escapes a group of bullies by walking another route, he uses it to cheat on tests, etcetera. However, his sudden prowess is noted by a beautiful, smart girl in his class called Yuno, who, it turns out, is obsessively in love with him and has been admiring him from afar for a while now. She also has a terrifying violent streak. Yuno explains that her diary is the Yukiteru Diary, which gives her details of what Yukiteru does day in and day out. Yukiteru and Yuno's Diaries work in tandem with each other, and that this game has now become a battle royale with 12 participants fighting for Deus Ex Machina's throne.
As other diary users come into their lives and nobody can be trusted, Yukiteru and Yuno are going to have to work together... even if Yukiteru really doesn't want to.
This manga is absolutely thrilling. I never read it before I watched the anime, but I started reading it after episode 3 or 4 of the anime came out, and haven't looked back since. I haven't finished it yet, but hey, I've been busy. Them's the breaks.
I love the survival/battle royale aspect of this manga. And I love how Yukiteru and Yuno's life permanently warps simply because of the choices they make in the game. Already Yukiteru has grown as a character, he's no longer a complete and utter drip, and Yuno still scares the bejesus out of me in tense situations.
There are 10 volumes of the manga available in English, but unfortunately the publishing company, Tokyopop, closed its operations before the final four volumes could be released. A shame, since the eleventh was set for release in September. x_x Plus, the first few volumes are very expensive for manga. We're talking upwards of £20 for the first few (and the tenth) volumes. Sad but true.