The White Plague

There were bodies everywhere. Bodies ripped limb from limb. Beasts of the night feeding on the dead. Within the span of a few days Japan's population was dropped to zero, moments after a castle had appeared in the night sky.
It started when the castle itself dropped down, crushing buildings and people below it. The people who weren't running away screaming, stood stiff and pale as a being walked from it's front doors. It was a young adult. Silvery hair glowing under the light of the city around him, with a face enshrouded in darkness. He seemed... godly. Like no other person on this earth. An aura radiated off of him, dark, terrifying, imposing. In a slow motion, he raised a hand forward, pointing towards the crowd, and a word, a whisper, echoed across the city into everyone's ears.
Feed.
A moment after the word was uttered, howls erupted, screeching as a tidal wave of shadows erupted from every crevice of the medieval fortress. The people closest were engulfed, evaporated. Bodies ripped apart to nothing. The beings tore threw everyone in sight, devouring everyone. Within minutes, the city's populous was gone. Man, women, children. All were gone. And then the others came.
Even with a call for evacuation, the countries population was dropping by the hundreds, second by second. Buildings burned as skeletal wyrm's threw fire down from above. Hordes of undead roamed the streets, compacting them and turning those foulish enough to try and hide. When Japan's finest came in their tanks, gun's blazing, their tanks were ran through by blazing steel bladed wheels, as their infantry screamed, while durga and other beasts slashed through their ranks.
Even as hours past, people there and around the world realized that the night sky stayed it's same pitch black, as the king of darkness made it's presence known. Word got to other countries, who barred travel to the country now gone, as their leaders came to formulate a plan, ensuring those who knew the end was near that
"All would be okay. The threat will be stopped, and the dead will be mourned."
but not a soul believed them. Pilots in speeding planes flew in, shooting through the skies, trying to lessen the number of beasts that endlessly poured through the island nation. When the call for nuclear power was given, people cheered, watching as the bomb dropped, before any person watching their screen dropped their jaws, speechless and horrified as monstrous being of white flesh, the likes of nothing seen before, broke though the keep's tallest tower and rose to meet it, sending it away within the span of a second.
The camera, miles away, laser-focused on the young man, still standing their beneath the castle, who stared into it. Before disappearing, with the castle and it's monsters along with it. Silence punctured the planet, as the camera went static, wondering if it had decided to give the planet peace, whatever that god may be. People flicked through channels of the news, to see anything they could find, before all went to a single station.
He stood there, in front of all the world's highest, as the castle appeared once more, crashing into the UN building, as the world learned it's first and final ultimatum.
They would either be corpses, or livestock. But no one could stop what was to come.
A new dark god had stepped down to earth.