Oretachi ni Tsubasa wa Nai - Under the Innocent Sky

This might just be a "what if" but, A certain day, Gretagard's pure white sky was overrun by winged ones. Now, the sky extends just about anywhere and everywhere, right? So no matter how far you run, you can't escape those white wings of theirs. And that's why the people without wings went looking for a sky of their own. Their prayers were listened, and they are now listening to "Jingle Bells...