Storm Dragons are the masters of the skies. They are excellent fliers and land only to rest and eat. In addition, they have full control of the weather. They are very hot-tempered and easily angered. They will attack any human that bothers them, conjuring strong winds and dangerous lightning.

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.

If Avias Skylier is the cave's "watch dog," then Atmosil Cumulon is the "guard dog." Since Avias Skylier patrols the outer rims of the territory, Atmosil Cumulon flies in the areas nearest to the cave itself. If she hears Avias Skylier's alarm, or if she catches a human or dragon that somehow managed to sneak past him, she won't hesitate to throw everything she has at the intruder. If she needs help (which is uncommon), Nyxia Ebonox will always be the first one to fly to her aid. Like all gray dragons, Atmosil Cumulon is extremely short tempered, so April and the other dragons usually don't bother her. However, she is very protective of all the inhabitants of the cave (both dragon and human), and would readily sacrifice her life in a fight so that the cave would be safe from the threat.