- The gaichuu and how they eat hearts. In the manga, this happens to Lily Confort on-panel.
- 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 killer insects called Gaichuu.
- Having their Heart devoured by a Gaichuu causes a person to be reduced to a mindless, emotionless shell that can do nothing but sit staring into space until they starve to death.
- The man-made sun is alive. And it occasionally feeds on the citizens, taking away portions of both their bodies and their hearts.
Nightmare Fuel / Letter Bee