Nightmare Fuel / Tegami Bachi: Letter Bee

• Amberground is a truly awful place to live, perpetually shrouded in darkness except for a small artificial sun over the capital and infested by gigantic, Nigh-Invulnerable heart-eating killer insects called Gaichuu. A person whose heart is devoured by a Gaichuu is reduced to a mindless, emotionless shell that can do nothing but sit and stare into space until they starve to death. In the manga, this happens to Lily Confort on-panel.
  • Also, Amberground's artificial sun is alive - and it occasionally feeds on the citizens, taking away portions of both their bodies and their hearts.