Dorsal Dragons are so named because they have large fins along their backs that can be raised and lowered at will. They use these fins to regulate body temperature; they raise them to cool off when they become overheated. The bright colors on the fins double as a means of attracting mates.

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.

Dark Woods Circus, like most of the Vocaloids, has a dark and twisted past: the difference is that his evil deeds still continue now. He lives, as his name suggests, in the middle of a dark and forbidding forest where few living things dare venture. There, it is rumoured, he keeps deformed and mutated dragons in cages, observing their suffering for his own amusement. His is not the only twisted mind to find a perverted fascination in the 'freaks' he collects, and other dragons pay him for the chance to gawp at the captives. Dark Woods is a large Dorsal Dragon, ten metres tall with his fins fully raised, and his eyes are wide and glow with the intensity of madness. Despite his insanity, Rin Kagamine has for some reason fallen for him, and she killed his former mate in order to earn his affection. He tends to be as cold towards her as he is towards everyone else, but Rin doesn't care one bit; all that matters to her is that she is now his mate.