Tenshi Kinryouku: Tokyo Chronos

The story centers on Kuon Kanae, a junior high school student who was in Tokyo on the day white feathers fell. Kuon sometimes sees feathers on people's back, and sometimes sees the sky filled with black letters…

(Source: Anime News Network)

Note: The manga takes place after the story of Tenshi Kinryouku (Angel Sanctuary), but it is an independent work.