Think of this as a Death Note meets Fate/Stay Night meets Battle Royale.
In the world where people are attached to their cell phones (Oh hi Japan), a boy named Yukiteru gets involved in a "Battle Royale"-esque game. He and several "Diary Holders" must kill each other off; the winner will become God/Deus Ex Machina. Each carries a diary: cell phone, picture book, scroll, whatever. Although, these diaries aren't exactly normal. They tell the future, or sorts there of. For example, Yukiteru's Diary tells the future of those around him. Whereas another's might describe any future ways to escape death. The problem is, is that Yukiteru isn't a very strong kid. In order to survive, he might just have to rely on Yuno Gasai, a crazy, sadistic, love-struck stalker. How much should she trust her, when she's practically the epitome of a psychotic serial killer?
Yukiteru Amano - A bit of a social recluse-type of boy who jots down his diary in his cell phone. When he's alone, he talks to his "imaginary friend" Deus Ex Machina, who turns out to be... not so imaginary. He's a bit of a wimp, so he probably can't survive the game without help of his friends, or even Yuno.
Yuno Gasai - Crazy crazy crazy Higurashi girl who will do anything for Yukiteru, even if it means killing everyone else (while smiling). After all, she stalks him constantly. She has some hidden pasts though stored in her closet (or room), and who knows? Her affection for Yukiteru might be a little too much for society to handle.
Deus Ex Machina - God. A very huge creature who is only visible to the "Diary Holders". He creates the game for the Diary Holders in order to determine who will take over his role of God.
Probably my favorite manga that hasn't been turned into an anime yet. Mirai Nikki excels at creating suspense and plot twists. If you like that type of stuff, go read it. Also, Yuno is a great yandere =)
Additionally, if you want to read more into the life of the characters, you might want to check out Mirai Nikki: Mosaic.
Anyone else read this? Favorite characters, comments, complaints, etc?