Deus Ex Machina (the god of time and space) creates a death game with twelve participants, the last one standing alive will inherit his position as god. To make things interesting each is given a diary (cell phone or paper version) that predicts the future. Though fate is always changing, it is hard to keep up and stay alive.
Yuki is our antisocial hero who develops an unfortunate romantic relationship with fellow participant Yuno, a "slightly" deranged stalker girl. With only one who can live, no way of bowing out and everyone else trying to kill them, will love conquer survival?
This series does not shy away from anything. Each character is mentally and physically scared, you never know what they will do next and your opinion of each is always changing (just like the future). I think the way they have juggled each personality and developed them is amazing and almost unique to this anime (no other series has done it this well). The story is twisted, you cannot predict (ha ha) what's coming. Finally the general feel *shiver* it's thrilling, scary, funny, revolting and suspenseful.
Great art, awesome music (hint; if you listen to the second opening song which is in English, it tells you everything) and smooth story telling.
Must watch! Only if you're old enough.