Reaching this final episode of Haibane-Renmei, the thing that took me off guard the most was the revelation that Haibane-Renmei is Reki’s story. It took all 13 episodes to realize Rakka is a second-person perspective to Reki’s tale, and a catalyst to Reki’s change, both planned and at the same time unplanned by Reki.
Reading that I feel a certain vindication of my worldview, because this is how I think about Haibane Renmei's structure too.
At some point I thought that it's somewhat common to displace the observer or the narrator. Consider Kyon in Haruhi, or Mikan in Manabi. Rakka is a purer application of this technique. But I appreciate how she's not just ABe's exposition tool, and how her own story is very important too. It all was exquisitely designed and implemented.