When Water Dragons mature, they lose the ability to survive on land, entering the water permanently. They are adept swimmers and eat whatever fish are in the lake they live in. They tend to inhabit the same lake for their entire lives, although a few live in the ocean and swim all over the world.

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.

He has been given the name of the Greek Sea God Poseidon and the epithet "Ryuusuisei" or "Dragon Water Star", because he lives in water bodies.

It is said that the areas, in which he inhabits, there are the cleanest water and the rarest sea creatures available.

Regarding fishes as his own subjects, he claims that it is his duty to protect them. If humans dare to enter his domain, especially for the sake to fish, then he does not hesitate to take actions. He wraps himself around their ships to sink it and pulls the humans with him, leaving them to be perished by drowning.

Poseidon is a violent and a cold-hearted dragon. He had once enslaved a nearby village, which were forced to give him a young maiden every year as a sacrifice once a year. In return they were allowed to fish in his water. However, they did not keep their part of the bargain. Therefore, he deluged the whole village, drowning everyone who was present there.