Hellfire Wyverns are so named for their foul tempers and fiery visages. Their social structure places all females above all males, due to superior physical characteristics and violent dispositions. Forced subservience of the males causes them to become vicious, petty, antisocial, and passive-aggressive compared to the aggressive and social females. However, orphaned hatchlings raised by foster parents of another species can develop surprisingly even tempers and mellow dispositions, proving that their defining unpleasant nature is, in fact, a learned behavior.

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.

Contrary to most Hellfires, you need to look for the most aggressive of his breed's females to find someone as strong and prone to fighting as Grimmjow. Although in his case it helped that he was the first Hellfire in the clan, and therefore, there were no females to boss him around. Grimmjow's always seeking strong opponents to beat down, and he found his perfect match in the form of the Night Glory, Ulquiorra. Grimmjow immediately took a disliking to the other stoic dragon, and so he vowed to defeat him, a difficult task since the Night Glory always manages to be faster, evading Grimmjow's flames until he tired enough to be considered defeated. As time passed, their hated enmity became a respectful rivalry, with them acknowledging the other's strength. Still, Grimmjow is always going to be bitter at the fact of having to babysit his rival's hyperactive son.