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.

Hydro Boy lives mainly in rivers, but will sometimes go out to sea. He is the leader of a gang of water dragons called "The Jolly Rogers". As their name suggests, the Jolly Rogers are a group of buccaneers with a fearsome reputation. Whenever a ship passes through his territory, Hydro Boy calls upon his gang and they attack it. This is usually done by ramming the ship until it sinks or capsizes, but they can also create whirlpools to take down tougher ships. Any humans caught up in their attacks are usually left to drown.

Once the ship has been sunk, the Jolly Rogers will raid it, taking any valuables they can find. The booty is then divided between everyone. Since Hydro Boy is the "captain" he always gets most of the booty. Hydro Boy is usually quite fun loving and enjoys being a pirate, but he shows no mercy to anyone who crosses him.