Small headcanon time: while obviously, the fleeing Mhaci and Amdapori mages within Gyr Abania created Red Magic, the Hyur and Elezen who would form Gelmorra were also quite inventive, if also desperate. For fear of drawing the Elemental's gaze to their home beneath the soil, magic drawing from the surrounding aether was banned. It wasn't worth drawing their ire, when they understood how to craft healing salves and splint a broken leg.
However, the more time passed, the more the blossoming nation realized they needed some form of aetherial manipulation, and they needed something more powerful than what they'd developed so far. Sure, they were capable of minor feats, but what would happen if they needed something more major than harnessing crystals, or teleportation? What if they needed to heal themselves? What if they needed to fight? As such, a small collective of Hyur and Elezen realized that if could use their own Aether as fuel, then they should be able to sacrifice more Aether than they could passively replenish to cast spells of greater strengthâa greater, more permanent sacrifice allowing them even greater strength. This would shorten their life span, but allow them to replicate the might of an Amdapori white mage. Was the tradeoff worth it? Should somebody be expected to give up their life, for the sake of another?
Much time was spent debating the pros and cons of this form of magicâwhile the mages who fled to Gyr Abania would've begun to develop Red Magic and figure out the limits of using their own Aether, the people of Gelmorra would eventually decide the rewards outweighed the risks of their own developing magical system. When a massive structure in Gelmorra collapsed, injuring dozens of vital workers, these conceptual mages stepped in, each sacrificing major amounts of their Aether to heal those injured. By the end of the week, everybody involved in the accident had made a full recovery, and the structure was fully repaired.
This style of magic was defined by the sacrifices necessary to perform it, and as such, it was quite heavily regulated, both in when it was allowed to be used, and who could even be taught how to use it. Only in times of extreme crisis were these few mages expected to show up, but each and every time they stepped forth and performed their magic without any hesitation. It was a luxury when one of these mages could go their whole life without casting one of their spells, but there were also times where these mages would shave collective decades off their life span for the greater good. These mages were hailed as heroes, and treated with the utmost respect.
Understanding that their form of magic drained the lifeblood from their very bodies, a name was posited and subsequently adopted for this style of magic: Haemomancy, better known as Blood Magic.
Now, following the collapse of Gelmorra, Haemomancy is an almost entirely dead art. Very few even know about it, and fewer still attempt to practice it due to the inherent danger it brings to one's life. It is almost exclusively practiced by Duskwight Elezen who still reside within Gelmorran ruins, though a few of the Redbelly bandits who roam the Black Shroud also remember the once-prpud art. In the current state of the world, this self sacrificial style of magic just isn't necessary, especially now that elementals won't smite you for daring to draw aether from the world around you. Still, there are some few people who believe Blood Magic is worth remembering, even if Red Magic is a much safer alternative.