Fragile - Sayonara Tsuki no Haikyo(2008)

Fragile - Sayonara Tsuki no Haikyo

The story is set in a post-apocalyptic near future Earth that has lost its light and is covered in a dense fog. Almost all the world's population has vanished, and the cities have been left abandoned. After his "grandfather" died, Seto, a young boy, decided to set out in search for other humans.

(source: Wikipedia)