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.

Formerly a lone ranger, Tankrelli used to restlessly swim around the bottom of the ocean floor. Due to his sheer boredom, he would pick fights with other sea-dwelling dragons and wouldn't stop fighting until he got bored again.

He was later approached by a Guardian of Nature who decided to live in the deep waters just like him. At first, Tankrelli tried to pick a fight with him, but the GoN patiently dodged all his attacks until the Deep Sea dragon got tired of charging at him. The other dragon merely said that he wasn't looking for a fight and only wanted someone to help him protect the surrounding area from trouble.

This gave Tankrelli an excuse to fight other dragons, but the more time he spent with the GoN, the more peaceful and self-controlled he became.

Tankrelli now works alongside the Guardian, helping him defend the ocean from anyone that threatens it.