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.

Platino found Tranquilus' egg one day when he was mindlessly flying along, since it was distracting him. After hatching, he became even more annoyed with Tranquilus' aura since it makes it hard for him to concentrate, but soon they became fast friends. Tranquilus helped Platino calm down on a particularly stressful day. Tranquilus likes to play games like chess with Platino and he always makes it hard for him to concentrate and win.

Tranquilus' name is denunciated from the word "Tranquil".