The Fiery Sword is a sword with an inherent Fire Aspect I enchantment.
It does 6-8 hitpoints of damage.
The Fiery Sword is part of the tools and armor made from fiery ingots, which require Fiery Blood and iron to craft. Fiery Blood is a drop from the Ur-Ghast and the Hydra. This is from the Twilight Forest mod, and this sword can occasionally be found in Twilight Forest loot chests.