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.

His nickname is Mari, which, yes, does get a little confusing for those who don't personally know him. Mari is a reserved, generally solitary Deep Sea. Like others of his breed, he sticks firmly to the deep trenches and seafloor around his home, only surfacing when his mother starts embarrassing herself. His mother, Oarfish, is kind of an anti-Deep Sea. She prefers being on the surface and tries her best to stay up longer to interact with more diverse breeds. While her other children just accept this as an oddity, Mari legitimately worries for her over it. He knows it goes against what their breed is by nature and thinks she'll hurt herself if she keeps it up. He has been trying to convince her to give up her efforts and live "normally", but these efforts have mostly gone in vain. Needless to say, Mari inherited Oarfish's stubbornness because he hasn't given up trying to help her. This results in the two having an odd sort of rivalry to see whose will wins out in the end.