Mancers using Nivium and energy in tandem to aid in the manipulation of fire.
The legend says that in the devastation that an Abassi Stormrider brought down upon a village that did not pay its due tribute in the land that would become Romatuos set the place afire, the peaceful man named Roh who had eaten only wheat and fruit his whole life and never set his hand to violence watched his wife and 8 children be consumed by the flames, but with the Nivium amulet around his neck that was to be the tribute the fires would not touch him, they whispered to him instead.
In that moment he screamed to the heavens, and his breath was fire hotter than the sun, it lit up the sky and before the cowardly Stormrider could escape his mount caught alight and streaked across the sky landing at the feet of Roh himself. He burned the rider to ashes in seconds and even as the fire crept up the feathers of the Golden Horus Roh ripped its heart out with his bare smoking hands and ate it.
From then on it is said Roh could spread about him wings of flame, and flying above his vanguard he went on to lead what would become the sons of flame to victory after victory against the Abassan empire, who soon came to fear this new Fyremancery and be apprehensive about deploying their valuable Horus' against him. But of course this is only a tale, a tale every boy in the old Romatenuon empire learned of their origins.