Deep Sea Dragons, as their name suggests, spend most of their time in the darkest depths of the sea. They have a bioluminescent dorsal spine that serves to attract prey and communicate with their own kind. As with many deep sea animals, they generally eat whatever they can manage to bait. They rarely leave the ocean floor, surfacing only during breeding season. When they do choose to travel to the shallower depths, they avoid bright lights and will only come up far away from shore.

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.

Isothermal is an outrider among his clan, rarely surfacing to interact with them (although as there are plenty of shadows under the sea, he gets along quite well with Ghost's Dancer). Instead, he lurks beneath the depths with the other Deep Sea clan dragons, ranging the ocean floor for food and watching out for danger. Isothermal is a very cautious, careful, serious dragon, with no patience for any kind of fun or games. While he loves his clan, he prefers to be alone, and dislikes that the other Deep Sea dragons in the clan look to him as a leader. However, he rises to the challenge reluctantly every time, because however reluctant he is, he's a good leader and ferociously protective of his clan... even if he doesn't show it.