No one expected it, not a single human being who woke up that day could have known what was going to happen to them, but the pokemon noticed, around the world each and every one of them seemed to be acting weird, timid, scared of something. Around the world sightings of legendaries were reported, Lugia, Ho-Oh, Zekrom and Reshiram, even the ever elusive Mew and MewTwo were seen, looking off into the sky, they knew something was coming. As the crowds gathered to observe the legendary pokemon, something loud caught their attention. It wasn't an explosion, it didn't sound right. It was like part of reality itself was shattering, the sound was heard from Kanto to Unova. Those close enough to Mt. Silver could see darkness spreading from the mountain's peak... smoke? clouds? Whatever it was it rose into the sky, blocking out the sun as it spread over the world. Some had claimed to have witnessed Arceus at the top of Mt. Silver combating a large, bird-like pokemon. It stood on two legs with taloned claws and feet, it's body covered in black feathers with red markings over it's body, black wings protruding from it's back. The few that saw it, looked into it's red eyes could barely contain their fear. Even a glance seemed to be enough to deteriorate the strongest of men. It was obvious this darkness was spreading from it. The pokemon god clashed with this... 'demon' as it was to be called but no one stuck around to observe the conclusion as the dark skies began to drop rain upon the world. It fell for days, weeks, but this rain didn't cause floods, it was unnatural, whatever it touched began to dry up, it wasn't long before all forms of plant life died, and then the pokemon began to disappear. It was first thought that they were dying off, but there was no evidence of this, no bodies or remains. The more religious claimed that Arceus remvoed them from the world, protecting them until this disaster ended. Unfortunately, no human being lived to see if this was true or not.
Eventually life returned to the world after mankind fell, once he deemed it appropriate, Arceus returned to the world, looking up on the newly grown plants and ruins of man. The loss filled him with sadness, he truly regretted abandoning man, but it took all that he could to save the world's pokemon. He did not realize how powerful it had become these long years it had been locked away, hidden on the mountain. He had underestimated it, and blamed himself for this. The pokemon god summoned the legendaries around him. "It seems that the worst has come," he explained to them all. "The world of man is no more."
"Then we are free," MewTwo replied, crossing his arms and glaring at the god. "This world belonged to us from the start, they took it from us once they gained the ability to capture and controll us like slaves."
Arceus glared at him, "Silence," he demanded, "You're lucky that I did not smite you long ago. Regardless of your opinion of them, mankind was our companion. We shared this world with them, so show some respect."
MewTwo continued to glare at Arceus but held his tongue as he went on. "And in respect for that loss, I have made a decision, one that will allow us to continue to survive." As he spoke a light enveloped him, similar to the light that envelopd a pokemon during evolution. The others watched as Arceus changed shape and as the light faded, it revealed a new form, not one of a pokemon but of a man.
"You can't be serious," MewTwo burst in again.
"Doing this not only effects us," Lugia interrupted, "It will also effect it, the one that did this."
Arceus nodded silently, "It has gone into hiding, but doing this will draw it out, anger it. This is also about population, in these forms we can expand farther than we could normally. I know this change will be difficult but I ask that you trust me."
The rest of the pokemon were silent as they too underwent the transformation. "So..." Entei said, taking in his new form. "What do we do next?"
"Rebuild, of course," Arceus said as he looked out onto a broken city as he began to return the rest of the pokemon to the world, giving them new forms as well. The process would take a very long time, but it would be worth it in the long run.