'Like all the Haibane, Rakka emerges from a cocoon looking like a normal girl—at least until she sprouts her wings and is presented with her sizzling fresh halo. Like most of the angel-like Haibane, she's filled with a sense that she used to have a family and an identity, but she can remember nothing about her former life, including her name. The other Haibane call her "Rakka," based on the dream she had just before hatching, and they kindly explain how her new world works.

In the rustic world of Haibane-Renmei, the Haibane—the name translates as "Charcoal Feathers," and refers to the color of a Haibane's wings—live apart from humans, in accordance with the rules laid down by the Haibane Renmei ("Charcoal Feather Federation"). They must have jobs, but must not accept money; instead, they keep track of their "earnings" and "purchases" in notebooks. They must live in places that humans no longer use, and use only the things humans no longer need. Above all, they must stay away from the monumental walls that surround their city and pen them in. No one, human or Haibane, is permitted to pass outside the walls.'

- from scifi.com