This is a beautiful start of what is to be an amazing anime.
To really understand this anime, go into this thinking that it is all prequal to the real story which is Hiiro no Kakera: Dai Ni Sho (2). I would suggest watching the first 3 and the last 3 episodes of this series. All you really need to know is the characters and the base plot. After you got it, please watch the next Hiiro no Kakera season. It's anime you do not want to pass up just because the fist season was inferior.