This show is f*cking incredible. I love every bit of it. The story is original, the characters are a bunch of mysterious kids, the opening theme is gorgeous and the animation is breathtaking. It is a perfect combination of drama, mystery, sci-fi and action. The fillers are also well and it actually feels as a whole. I really can't tell you much about the whole plot because that would mean ruining it's originality. Just try watching 3 episodes of this and I promise you that you won't be able to put i down. It is a little confusing but trust me, it is incredible.