A sword once forged to fight spirits, now wielded by a spirit.
Wraithbane was forged by a great Dwarven swordsmith and enchanted by powerful mages as a gift to King Arcturus Marwood, ruler of the land of Haraldin, to lead the fight against invading Undead forces from the cursed kingdom of AutumnsReach, ruled by a lich who usurped the throne. Though the attack was successful and the lich's phylactery destroyed, King Marwood himself was struck by an arrow.
His sword was entombed with him in a temple built into the back of a giant earth elemental (to prevent thieves from taking it), resting in a preserved state as his body rotted away for three centuries.
For all that time, Wraithbane lay dormant, waiting for the return of its king...
King Marwood's soul was afflicted by the curse over AutumsReach, as a result of falling in battle within that bleak land.
While most rise as a skeleton, ghoul, or mindless zombie; Arcturus was unable to reach his corpse, and so he he wandered the earth between this plane and a strange, empty limbo as nothing more than a shadow. When he made it to his tomb, he found his corpse to be sealed off from both the living and the dead, he was forced to bind himself to his armor. Thus, he rose again as a phantom, a shadow of an age long gone.
He took a hold of Wraithbane once more, and it felt his presence. Once again it glowed and sparked with power, willing to slay anyone standing in its King's way.
He wandered to the fog-covered, shadowy lands in which he fell, and went back to the throne room where he confronted the lich.
He cast aside the crown of Haraldin and donned the crown of AutumnsReach, declaring himself the once and future king of the Damned.
Long live the Phantom King.
(Wraithbane is a zweihander, btw.)