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.

Deiyume Tatsu is Japanese meaning Day dream dragon. He is very smart and prefers the phrase "brain over brawn" to "body over mind" when it comes to any sort of combat, not that he fights often. In fact, Deiyume Tatsu hardly ever fights any of the other dragons in the cave. He's the right hand man of Hogosha-tatsu, the dragon clan leader, and loyal follower of the clan master. He sleeps most of the time and likes to toy with the more "simple minded" dragons by giving them "day nightmares" rather than day dreams. Dieyume Tatsu gets a lot of dirty looks because of this habit, but the clan master stands up in his defense. He is awiating a mate, which he hopes will be a day dream dragon like him. Deiyume Tatsu and Yumetatsu became mates shortly after spring began and both are day dream dragons.