Waterhorse Dragons received their name due to their horse-like physique and endearing behavior. They are capable of surviving out of water, and when on land their skin secretes a gelatinous goo to retain moisture. However, their large paddle feet are better suited for swimming, and waterhorse dragons tend to move very awkwardly when on land. Waterhorses are very friendly dragons and enjoy playing with humans.

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.

Umi no Uma is part of the water dragon royalty, or the Blue Kingdom. The Blue Kingdom consists of, of course, Umi no Uma, Bagu no Kawa, Kurai sora ya ame, Kawa no kurai, Kawa no tsume, and Arashi no hi. The king and queen are Arashi no hi and Kawa no Kurai.

Umi no Uma has bred with Kingu suija. Their child is Sotsu of the Silver Dream.