The Emperor's Flaming Sword is the weapon the Master of Mankind bore in the last, terrible hours of the Horus Heresy, when He teleported aboard the Warmaster's battle-barge to end the rebellion that had broken the galaxy. Wreathed in psychic fire and forged by arts long lost, it was with this blade that the Emperor at last struck down His favoured and most traitorous son.
The sword blazes with a light that is more than flame, an expression of the Emperor's own boundless will made manifest as a cutting edge. It parted daemon and traitor alike upon the black decks of Horus's ship, and its fire is said to have seared the very soul of the Warmaster before the deed was done. In an age when the Emperor sits enthroned and silent, the blade endures as a relic of the last time He walked and warred as a living god.
Among those entrusted with such holy inheritances stand the Adeptus Custodes, the golden guardians who kept the Emperor's side through the Great Crusade and keep His Throne still. To them the memory of the flaming sword is sacred beyond words, a reminder of the day their master fell and yet triumphed. The blade is faith and fire and sorrow together, the weapon of a god who gave everything to save a species that would spend ten thousand years failing to deserve it.