The Witchblade

A heavy, two-handed greatsword of dragonborn craft. It was fashioned sometime in the third century for Ser Avarax the Red, a commanding general of the Knights of the Red Scale. At this time, it was capable of bursting into flame to scorch the knight's foes, functioning as a +1 Flametongue greatsword.
The sword was gifted to a pupil of Ser Avarax, however both the pupil and Ser Avarax himself were slain during the War of the Red Scale and the sword was lost, until its rediscovery early in the fourth century by the Vampire Saaya. Over time, Saaya's own black magic seeped into the blade's metal and the sword adopted darker powers, reflecting its new owner.