What is the blade of khaine?

Here goes the quote from 5th ed. HE book. There is much more, but I can't type the whole text, it's too long. But even this extract should explain a lot:

"From the beginning of time it had waited, embedded in the great black Altar of Khaine on the Blighted Isle. The weapon was old as the world and deadly as poison, a shard of the fatal weapon forged by Vaul Himself for the death god Khaela-Mensha-Khaine, a fragment of crystallised death capable of slaying Daemons and gods alike. No mortal could wield it and live, but Aenarion had passed beyond hope and beyond despair. He lived to slay.

Caledor knew what would happen and tried to warn Aenarion. He told Aenarion that he would be cursed if he drew the weapon, that such power was too great for any mortal being, and it could only be bought at the price of Aenarion's immortal soul.

Seized for a moment by the power of prophesy, Caledor spoke words that would ring down the ages. He told Aenarion that if he sought such corrupt power he would bring eons of tragedy to the Elves, that he and his line would be accursed to the last generation, that the gods would turn their faces from him and that Aenarion himself would surely die. The first Phoenix King made no response, merely climbed onto the back of Indraugnir and flew off into the dreadful night."