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.

His name means "Water" in Japanese. He was raised by his adoptive father Kaito, along with Kaito's daughter Sazanami. He used to be very shy and didn't really like to interact with the other dragons in the colony. He's very protective of his sister and originally didn't like her mate, but he's warmed up to him and they are now friends. Mizuru really broke out of his shell when Sazanami introduced him to her friend Sora. Her fun spirit convinced him to become more social, starting with her. They began hanging out and soon they fell in love. They became more serious and began courting, and eventually they became mates. Mizuru always figured that he'd eventually have a water dragon for a mate, but he is glad that he met a beautiful Skywing instead. They are so in love, and look forward to spending the rest of their long lives together.