Shadowdancer

''The weapon seems to move your hand on its own, rocking it side to side in rhythm to a song you can't hear. You experience a brief vision of a figure perched on a high wall dozens of feet off the ground, overlooking an impressive castle. Judging by the style of the buildings around it, it is unmistakably Jirrahl. You hear a door swing open below you, your target dressed in a thick flowing robe of gold and red, their hair long and black like the feathers of a raven. You descend, a practiced art of your clan, plummeting like a bird of prey. The instant before you strike, you throw a small black blade at their guard, before landing on top of your target. Her spine crunches beneath you the wind leaving her body in an abrupt expulsion that includes an amount of blood and vomit that your masters never warned you of. It stuns you for a moment, the clashing of your blade fighting on its own, fending off and slaying her bodyguard. You draw your dagger and slit her throat slowly while reminding her of the debt she failed too many times to pay, your voice trembling as you do. Her bodyguard is ribbons, you recall the sword to your hand as you leap off the building and glide to safety in the waters below.''

Katana, requires attunement
This weapon is merely a dancing sword from eastern lands. It's black color may suggest darksteel, but it is not. You may have the weapon hover and make an attack at a target within 20ft as a bonus action. When using the weapon this way, it has advantage on weapon attacks made in darkness, magical or otherwise.