A figure stands there, almost limp as if it were a puppet, but standing tall and strong. It's eyes list lazily off to the side, and it's mouth hangs open just a sliver indicating that it is, in fact, dead. But still it stands, grasping onto it's sword like it were it's lifeblood, and keeping it rock-steady, depsite the figure's occasional swaying.
And the more you look at it, the more you feel that the sword, five feet of black and silver metal, is weilding the man, and not the other way around. It may have been in life that this man in his great suit of once-gleaming armor was a hero of great power, and he was when he was alive. When he was alive, he stood nearly seven feet tall and was a paladin of the highest order. His armor was mithral, to allow for movement, and his face fair. He was the very figure of a great hero, even his sword the purest of whites.
Then, everything went downhill, and from the way he stands here apparently having crawled out of his grave, there are a few obvious turns that were taken.
The sword still remains, absolutely still amid the swaying corpse grasping it, taking in the surroundings that the corpse does not. The handle was once wrapped in fine leather, but now is a few rotted strings atop a metal mesh. The handle was once solid gold, and now is adorned with hundreds of tiny, dried corpses of rodents and insects who touched it and died, coated in the blood of thousands. The blade was purest white, and now a streak of black lines it's center.
Six hundred and sixty-two years ago, while magic and knowledge were gaining promenence in the world, the gods looked down and were displeased. They could see that the forces of good and evil, of law and chaos were swinging wildly in power, from pure good to raw evil, back and forth with each one conquoring the other as they both gained in power. If this continued, they surmised, the world would end. They needed to remove some evil from the world, from the very stuff of souls, or it would crash into nothingness.
And so they forged the sword of souls. It was a sword so keen that it could cut through a mortal;s very soul, and seperate the good from the evil. The good would be released as the soul was always upon death, but the evil would be stored inside the blade. It was brought down into the world, and given to one of the greatest heroes of the time, the greatest paladin to walk the lands in years. He took the sword, and vanquished hundreds if not thousands of foes, trapping much of their soul-stuff within the sword, and releasing only the goodness back into the world. In this way, much evil was removed, both from the current day, and also from the rest of time, for the children of the next generation would be born without the propensity for the evil that the children of the year before were. It was only a temporary solution, but it worked for the gods.
But even the gods underestimated the power of souls. With thousands and thousands of souls, each one totally evil, jammed into the sword, they eventually fused together. This mass of souls got stronger each time a new kill was made, a new sickness was drawn out, a new vile creature removed. And eventually, it grew smart and powerful enough to seep out of the sword again. One day, much to the heroes surprise, the sword swallowed his soul. It brought a different insight, a rationality and intelligence to the chaos and evil that there was before, and it granted it power enough to control the body.
The paladin was now a tool of the sword, rather than the other way around, and for years he travelled the land, wreaking havoc on the perfect world that it had helped to build. It cut through across the multiverse and wreaked havoc across all worlds. And the gods fought back. They called back the greatest heroes iof the day, alive and dead and together the gods and heroes fought and trapped the sword in it's own demiplane, one with nothing in it, but empty darkness.
And then they collapsed the plane, destroying the sword for good.
But souls can exist in teh space between planes, for they must to travel to their final resting place. The mind and soul of the sword fell and fell until it was scooped up and put on display in hell. It was displayed as a collector of butterflies might display a rare, green variant, on a plaque, mounted on the wall. It was infuriating.
Even when it was brought back, truly it was not the same. The sword was not the original, and even though it still had much power, it was only a magic sword. It could no longer drink in souls as it could before, and it had to rely on it's minds worth of cunning, what little magic they could master together, and the pure strength that stems from being both evil and undead. The body was weak, but the mind was strong. It would win this contest, and claim freedom again. It would learn to drink souls again. It would become unstoppable, even by the gods themselves.