Arceus couldn't recall the last time something like this had happened. It had been slumbering, tucked away within his own pocket dimension, when a slight ripple in the fabric of reality woke it. Rousing itself, the God of all Creation set about observing his masterpiece, seemingly starring into the vastness of the void. Was it an ultra wormhole? They did occasionally happen. He had created the Tapu's, as well as both Lunala and Solgaleo, for this very reason. No, this was not one of them. The birth of a new, alternate dimension? No, all seemed the same as before. Had something been thrown out of balance? Where his enforcers, those that the humans call 'Legendaries', not doing their jobs? No, nothing seemed particularly bad. Just to be safe, the deity did a head count. To it's surprise, it came up one short. The legendary wasn't dead; that simply wasn't possible. Concerned, Arceus attempted to peer upon the pokemon in question. To it's surprise, Arceus found itself gazing not only upon it's creation, but upon the face of a human, one that it had both thought and hoped to never see again.
For only the second time in it's existence, Arceus felt concerned. It pondered it's choices. It could simply reach across space time and smite the human, but in doing so it would break it's own rules. It could send it's primary enforcers, Dialga and Palkia, to deal with the human. Past experience with this human, however, proved that this would be a bad idea. Then, Arceus thought about the one it had deemed a hero. A young boy, now a man, that had done much to preserve the balance of the deity's favorite world. However, things had changed. That human had changed. He had grown hard and in some ways callous. He needed molding. He needed to be challenged. Otherwise, the hero would never rise to the challenge presented by the Trespasser. Yes, Arceus knew exactly what it would do. It set out to change the course of the world it so loved, forever.
