Harkon's Sword

 is a unique sword that appears in. It is similar in appearance to the Blades Sword in the base game, but with a different guard (or tsuba). It has a unique enchantment, which only works if the wielder is a vampire and causes the screen to go slightly dark with each successful strike.

Acquisition
It is obtainable by defeating Harkon in Kindred Judgement, or by pickpocketing it prior to this mission with the Misdirection Perk.