|Episode 6 «|| 傷跡 / 病 / 冬の到来
Scar / Sickness / Arrival of Winter
|» Episode 8|
Rakka is very depressed after Kuu's Day of Flight, and stays away from the other haibane. Instead, she is keeping Kuu's room clean. She notices dark spots on her wings. While she's eating in town, Hyouko approaches her to ask about the light, and Rakka runs off. The others worry about Rakka and suggest she use Kuu's bed. They're also making wing covers for the winter. Reki notices Rakka's wings, finds her as she tries to cut them off, and treats her wings with a dye that covers the black spots. Reki tells Rakka about her own past, that she's a sin-bound haibane, and that she draws to remember her cocoon dream.
For a more detailed summary, read about episode 7 on Sekai no Hajimari.