Their head is very small compared to their body size, but their eyes look like two huge and humid white opals, slightly falling and giving them a sad but cute look. Just above their eyes there is a wet eyebrow sticking to the top of their eye-socket. It is black, looks like a very thin foam stripe and is used to drop water in their ever open eyes. A long lash under each eye guides the water away from the face after it has flown over the eyeball. This structure explains why they cannot survive if they are under the branches. In that case, their eyebrows cannot poor the water in their eyes and the lack of humidity turns them blind or one-eyed. Nightbells can draw the life out of the tree and store it in their body. As they can also store the daylight, they mix it with the life in their back and create a liquid called Water of Light.
They have two little straws that allows them to draw the life out of the trees. When the Nightbells die, they dry up and melt in the bark allowing the life in their back to turn into Black Blood. It becomes an ashy dark liquid that never reflects the light. Also, the extra water that drips off their eyelash streams along the trees and gives birth to new Nightbells. As the life the dying Nightbells have sucked has turned into Black Blood, when they melt in the tree the dark liquid goes into the bark as well. Even if they live in the Requiem it is this ability to receive the light from the real world that makes them so unique in Time City.