Fifty years after the imprisonment of the Dark Titan Sargeras…
Azeroth had not known peace for so long. In the aftermath of the battle for Azeroth, the Alliance and Horde had banded together and finally ended the threat of the naga and for many long years, the world was at peace. The Alliance and Horde had joined together under one banner. Both factions were dissolved and melded into one single faction: The Champions of Azeroth, in memory of Magni the Speaker, who had offered his hard diamond body to act as a conduit for Azeroth's power herself. With that last act of sacrifice, the threat of the Old Gods had been removed and inevitably, Magni passed on.
The druids and shamans of Azeroth had finally purified the wound in Silithus, and healed the land. Everything thought impossible had taken place. The Ren'dorei were welcomed back into Silvermoon. The Shal'dorei walked once more in the forests of Ashenvale. The Forsaken were reunited once more with their human families. The Sin'dorei walked proudly around Stormwind again. Lordaeron was cleansed, and it was renamed "New Lordaeron". It became a sort of marketplace, a place where all races could mingle together.
The Sword of Sargeras was bit by bit melted, the liquid Titansteel being cast into walls and new structures for all the cities. Portal hubs were opened all over key locations, each capital city was just a portal-journey and a short walk away from each other. King Anduin Wrynn and the new Warchief Varok Saurfang jointly ruled the Champions of Azeroth in benevolence and peace. The kal'dorei made their home in Val'sharah, and Val'sharah was shaped into a massive World Tree, named "Zindrassil". Darnassus was built anew in the tree. Azsuna was also swallowed up by Zindrassil. Stormheim and Highmountain were not taken, as the kal'dorei respected their wishes of solidarity.
As for the Barrens and all the desert regions, massive rivers were diverted into the areas, such that all areas now were lush and green. Now, Azeroth was all green and blue again. Peace reigned and it seemed that nothing could now stop Azeroth from enjoying an eternity of prosperity and happiness.
In a secret hidden cavern in Zindrassil, Archdruid Malfurion Stormrage slept. Ever and anon he walked the verdant paths of the Emerald Dream, now cleansed forever of the Nightmare. Suddenly, his feet slipped, and he yelled as he tumbled down a rocky ravine. This was all very wrong. Black, twisted tree roots, with red cores, stretched all over. Corruption. Malfurion called upon his entire powers and attempted to cleanse the roots, but to no avail. Then, a dark shape, overflowing with burning malice and hatred, lurched out of the shadows. Two malevolent red eyes blazed, and from a mouth unseen, a hissing voice spoke.
"Sssstormrage! You were very carelessssss, very carelesssss indeed. You thought the power of the Old Onessss gone?! You thought the Nightmare gone?! Sssssuch arrogance! Desssspair! For your ssssoul is now mine! Behold, the remnants of the Old Onessss' power is now mine! I am Corruption itsssself, and now, you shall serve me!"
Two tendrils of shadow shot out and bound Malfurion head to toe. He attempted to call out for aid. "Cenarius! Help m—" A tendril clamped over his mouth. Dark corrupting energy poured into Malfurion and the druid screamed.
"It issss pointlessssss to resist, my young druid."
A tendril wormed its way through Malfurion's ear and into his skull. Malfurion writhed as the dark magic did its agonizing work, but he could not cry out, and he could not move.
"Rissse, Archdruid! Rise, my servant! You will be the scourge of a thousand worlds, the might of the Old Onessss! I name you…Prince Kandrazul Darkrage, Herald of the Nightmare."
In the cavern, Kandrazul awoke. His skin was grey, and his body was surrounded by red energy. His eyes also blazed red. His mouth was filled with jagged fangs, and his claws dripped blood. As the Nightmare Prince gripped his staff, it was warped. The wings on his arm turned to torn dragon wings, and his antlers were like Nathrezim horns. His veins were red, plain to see against his ashen hide.
Malfurion was no more, shattered and lost by the power of Corruption. Kandrazul Darkrage was in his place. Several horrified druids and huntresses rushed towards him, and with a sweep of his arm, a scythe of red energy appeared, and struck down the night elves.
As he made his way to the Garden of the Moon, the Heart of Zindrassil, his struck down some, he corrupted those who were too strong. Kandrazul knew what he had to do. Reach the heart of Zindrassil and plunge his staff into the font of power at it. Wherever he walked, the land was blighted. Green turned to red, tree trunks turned black and twisted, Keepers and Dryads were either cast down or turned to the Nightmare Prince's will.
At last, the font of power. A shimmering pool of still water. It was a well, reaching many fathoms deep. The ancient power of the night elves, remade. Before it stood Tyrande. Tyrande, the single person who stood in his way and defied the power of the Nightmare. Kandrazul gripped his staff. A dense, choking fog sprang up. Creatures of the Nightmare lurched out of the mists, and they were terrible to behold.
"Malfurion, my love, what…what have they done to you?"
Tyrande yelled as she shot down the nightmare creatures with ease. That voice…a shred of his former self still remained within the Prince. Kandrazul wavered, then steeled his brow. He crushed the fragment of Malfurion within him, and he slammed his staff into the ground. Red fires sprang up, and mists flowed everywhere. Out of the darkness, his terrible echoing voice issued forth.
"There is no more Malfurion. Only Kandrazul. Kandrazul Darkrage.
Tyrande tried to call upon the power of Elune to guide her through the darkness, but the Nightmare was too strong. The dark shape of Kandrazul Darkrage surged forwards. A blood-red scythe appeared in his hand. Straight and true it screamed through the air. Such was the power and momentum in the strike that it tore straight through Tyrande's chest and throat, and ripped out of her side. Tyrande's mouth opened in a silent scream, and blood poured from her wounds.
"You…you…don't…have…to…do…this…" Tyrande slumped to the ground, watching helplessly as her lifeblood seeped out. The fallen Keepers salivated as they thought of succulent flesh to devour. Kandrazul retrieved his staff, and strode forwards to the font. "Azeroth is ripe for the taking. Their denizens live in peace. No one will come to their aid when the Nightmare washes over their land. Farewell, Tyrande Whisperwind."
And as the Prince said this, the last breath escaped the priestess' throat and she slumped to the ground, dead.
Kandrazul slammed his staff into the font and the water was stained red. A pillar of red energy shot into the sky and soon, the entirety of Zindrassil had been corrupted. As the Nightmare Prince hovered in the air and watched his nightmare armies assault key locations all over Azeroth, he smiled, baring his gleaming fangs.