Dark fire fiction could refer to a genre of fictional works that involve elements related to 'dark' themes like mystery, the occult, or the darker side of human nature, combined with the idea of 'fire' which might symbolize passion, destruction or transformation. For example, a story might be about a group of witches whose powers are associated with dark fire.
In the 'Dungeons & Dragons' universe, there is the 'Balor'. It is a large and extremely powerful fire - breathing demon. The Balor is often depicted as a fearsome foe with a whip of fire and the ability to spread destruction wherever it goes. It has been a staple in many D&D campaigns and related media.