Black Dragons are warriors. They are strong and capable in battles of force, but also ample magic users, capable of devastating opponents with their spells. Their bright eyes give them excellent night vision, which is why they generally hunt during the night.

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.

Heiji is a highly respected member of the Kyokos Vale Defense Force. This dragon is extremely competitive, leading him to constantly hone his fighting ability, but Heiji's greatest asset is his brilliant mind. Able to rapidly make connections and predict others' intentions, Heiji often reacts before his mind consciously recognizes danger, leading to behavior that seems highly impulsive. Heiji also tends to rank his personal safety far below his companions' or the completion of his goal, meaning that he often dives into the thick of things without considering (or possibly ignoring) the consequences for himself. Fortunately, his mate Seigetsu is always ready to guard his back. Outside of battle, Heiji has an upbeat attitude, but he suffers from foot-in-mouth disease and somehow fails to realize it. He never understands when others get upset with him.