Daydream Dragons are the hosts of daydreams and fantasies. They spend the majority of their time sitting on clouds, dropping daydreams down into the minds of people passing by. Humans who live near Daydream Dragons must be especially careful not to let their thoughts wander, or they could end up spending hours or even days in a trance-like waking dream state.

Dragons are highly-intelligent reptilian creatures that—from a human perspective, at least—appear to live forever. Many different varieties of dragon exist, each with their own unique qualities, habitats, and behavior. Adolescence in dragons is usually marked by the growth of a hatchling’s wings, although not all breeds of dragons grow wings and some breeds have other traits that indicate the beginning of maturation. In Galsreim, dragons and humans coexist peacefully.

Yume got her surname for the same reason her whole kind are called daydream dragons. She is always lightheaded and doesn't pay attention to what's happening around her like the rest of her kind. However when she hears that one of her cavemates is in danger or in trouble she wakes up and will do whatever she can to protect that dragon or hatchling, but will go back to daydreaming in less than a second after the problem is solved.