Haibane Renmei - Vol. 2: Wings of Sorrow (2003)

When a girl named Rakka emerges from a cocoon with a pail of angel-like wings and no memory, she finds herself initially disoriented. Soon, she learns that she has just become a Haibane, an angelic being, and resides in a mysterious walled city. In these episodes, a job at the library helps Rakka discover more about herself and renews her interest in the outside world. Rakka is also helped by a young Haibane named Kuu, with whom she becomes fast friends. However, when Rakka discovers that Kuu has begun to fade and eventually goes missing, it forces her to investigate and discover some surprising things about her new home.