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.

Leviathan Plesyou is the leader of the Plesyou, a large group of deep-sea dragons that live together near the main cave of the clan. He still follows Ryoujin Jakka, but since their breed isn't one to surface frequently, let alone swim to the shore, someone from within the group was needed to organize them, and Leviathan was chosen for being the founder. He takes his position seriously, being strict in some aspects of their life, but is at the same time understanding, fair and wise.