Many fans were raged because there were changes from its original manga, but i am completely disagree with them. In my opinion, A-1 pictures and their director did an incredibly good job, given you have to deliver the whole story in just 12 episodes. Despite the changes, the essence of the story itself is unaltered much. I think to do this anime justice, you'll need to watch it before reading its manga, and that is what I totally recommend you to do so.
