Ok, this is a new story, I'm still working on my other ones, but I wanted to do something else, that's how I work usually. This idea spawned from an idea of Ash catching a Grimm and sharing his aura with it, that led to thoughts of Ash's soul getting trapped in the body of a Grimm, which eventually led to this story, completely erasing the idea of catching a Grimm and making a new way for Ash to end up as a Grimm.

Also, just so people know, there will be no romance in this story, so don't ask about pairings.

RWBY is owned by Rooster Teeth, Pokémon is owned by Nintendo.

Story start!

Update 2/24/19: Chapter revised.

Prologue

"If I don't do this the tree will die, and so will the pokémon who live here!"

"Ash!?"

"I'm not gonna give up!"

"NO!"

"Ash!?"

"I need to do this!"

"What are you doing!?"

"ASH!"

"Stop! That's too much!"

"PIKAPI!"

"ASH STOP!"

Darkness…

Ash opened his eyes with a growling groan. What had happened to him, where was he? Glancing around he realized that he was in a forest of some kind, how had he gotten here? An uneasy feeling settling in his stomach, he looked around some more; he could not see Pikachu, May, Max, or Brock anywhere…

A sudden searing pain course throughout Ash's skull as he tried to remember how he had ended up in this place, as if the memories themselves were sealed off by an impenetrable wall that forced back his every attempt to retrieve them. Ash clenched his head, allowing his thoughts to drift away from the 'how' of his current predicament, before the pain started to subside.

That's when something about his hands caught his eye; his normal fingerless gloves were missing. Not just that, his hands were pitch black in color. Ash quickly moved his hands in front of his face and was shocked to see that his fingers ended in razor sharp claws, looking down at himself, he saw he didn't have any of his clothing; instead he was covered in pitch black fur. Looking around at himself frantically as feelings of panic began to set in, a sensation of something swishing around behind him hit, he almost had a panic attack when he realized it was a tail!

Running through the forest as fast as he could, the lost trainer spotted a lake in a small clearing. Swallowing all the feelings of panic and disorientation, his run slowed to a crawl as he approached the water, dreading what he would see in his reflection, but Ash trudged forward, but froze in his tracks just before reaching the water.

Though he would be reluctant to admit it, a spark of shame had begun to form in the pokémon trainer's stomach, in this situation where Ash was without Pikachu, or any of his Pokémon, and confidence would be most useful, he now found himself lacking the confidence to even look at his reflection in the water. Disappointment with himself was the predominate feeling that filled him now, above all others. With a final burst of determination, the boy pushed all his negative feelings to the back of his mind and forced himself forward to look into the clear water.

Ash almost jumped back in shock at what he saw, but managed to hold himself in place. He took several deep breaths in an attempt to calm himself before he reexamined what he saw: some sort of pokémon, that much he was sure of, but it was certainly not one he had seen before. Sure he encountered pokémon he had never seen before all the time, but they usually weren't his reflection!

Ash did notice a slight resemblance to a houndour in his new form, but it was only in the basic shape of the head and the dark fur. His new face was covered by what looked like a white mask with red markings on it. Lastly, he took note of his eyes, which were nothing but glowing, blue lights coming out of the mask's eye sockets.

His body was still vaguely humanoid, but he guessed that he could probably move faster on four legs. He also took note of the many, jagged, bone-like protrusions coming out of his arms, legs, and back.

In the face of this radical change to his body, as well as finding himself in this strange area, with no memory of how he had gotten there, all the young trainer's attempts to keep calm were quickly failing him, his breathing quickening as his transformed body tensed. It didn't take long before the pressure that was building in his mind became too much, and the boy-turned-beast couldn't help but let out a panicked scream.

Ash's eyes slowly filled with dread when a scream did not come from his mouth, instead a loud howl echoed throughout the forest. Ash shuddered before he attempted to say something; he wanted to say 'help' but all that came out of his mouth was a strange growling noise. Ash's new fear was confirmed: he couldn't talk. How was he going to explain this to anyone? How was he going to be able to tell anyone who he was? Or find any of his friends?

Ash could have possibly gone over his panicked thoughts in circles for hours, had he not been snapped out of it by the sound of rustling in the nearby bushes. The transformed trainer warily looked towards the foliage, silently hoping it was Pikachu, or perhaps one of his other pokémon or human companions. It was not; a creature that looked just like his reflection rushed out of the foliage.

Ash took a step back from this strange Pokémon, wondering if it might have been a transformed person like himself, perhaps even one of his friends. These thoughts were interrupted by about five more of these creatures, all coming out into the clearing and staring at him curiously. Ash took note of one difference between these pokémon and his new body: while his eyes were blue, theirs were all red.

The young trainer mentally considered what his options were; even if the chances that these were transformed humans like himself were slim, attempting to communicate with them was probably his best bet to finding his way out of here. Just as Ash was about to approach and attempt to talk to the unknown Pokémon, he suddenly felt his body tense up again, a feeling of immense dread filling him. Almost unconsciously, Ash took a step backwards, he didn't know why was suddenly feeling so threatened by these pokémon. They weren't acting particularly threatening, but something in his gut was telling him to get away, as far away as possible.

The unknown Pokémon kept their glowing red eyes on Ash's form as he moved backwards, and slowly began to move closer to him. Ash felt his sense of panic rising, with a small hiss he held up his hands defensively.

The dark-colored creatures paused, staring at the transformed trainer blankly, before their stances abruptly turned aggressive, snarling and baring their fangs and claws threateningly.

Shaken by the sudden change in demeanor of his pursuers, Ash lowered his arms and prepared to run, when he noticed something that gave him pause; his forearms and hands were glowing a faint blue color, seemingly emitting some sort of energy.

Ash barely had time to put any thought into what the strange glow could mean, as he found himself needing to dodge an attempt by one of the creatures to claw into him as it charged at him. He wasn't sure what to do as these pokémon surrounded him, growling and barking menacingly. He was out numbered, and he didn't have any of his pokémon friends with him.

One of the creatures tried to strike him again, almost on instinct Ash attempted to block the hit with his still glowing forearms, his eyes widened with surprised when the claws contacted his arm and no damage was done, the attack seemingly deflected by the glow cloaking his limb. Ash didn't know what to think about the appearance of this defensive ability, but he didn't have much time to, the creatures that shared his form were still surrounding him and looked like they were all planning to mob him. One jumped forward and Ash swiftly jumped out of its way.

He didn't know how he had managed it, but he had jumped quicker and higher than he ever jumped before. Ash noticed that the faint blue glow that originated on his hands and forearms had spread all over his body, and he felt powerful, so even powerful that his confidence was beginning to return as he felt how fast his body could move, and he bet he was strong now too…

A chance for Ash to test his thought came quickly as one of the pokémon charged at him, but this time he blocked it head on, before swiping his claws down and knocking it to the ground. The one to his left jumped at him, but he hit it away with his glowing arm. Ash spun around quickly and pounced towards one of the others and tackled it to the ground before charging off into the forest. The pokémon tried to chase him but whatever this glow was seemed to have made Ash far too quick for them to catch. He lost them quickly, but he didn't stop running until he was sure they couldn't track him down.

After a few hours of running Ash finally began to slow down. He gave a few heavy breaths as the blue glow that surrounded his body faded. Glancing around to make sure that no more of the strange pokémon were following him, before sighing in relief when he found he was alone.

Ash looked up at the sky and noticed that the sun was setting, and he was feeling rather tired after that chase. After another look around his surroundings his blue eyes settled on a large, hollow tree stump.

Ash approached the giant lump of rotting wood and felt a pang of disdain that he forced back; this was not the most ideal place to sleep but considering everything it would have to do for now. Ash managed to climb into the large stump before curling up in as comfortable a position he could, feeling a bit surprised when he found it was not that uncomfortable; it was not like a bed or anything, but he probably wouldn't have many problems getting to sleep, Ash briefly wondered if his new body had anything to do with that.

As the transformed trainer lay there, curled up in a hollow stump, he began to think about what he would do tomorrow; finding his friends was a no-brainer, but how would he explain what happened to him? What had happened to him anyway? And also, would they even be able to recognize him? Had anything like this happened to them as well? And how exactly would he be able to get back home, and to his original form even if he did find help? These, and many more questions plagued the anxious mind of Ash Ketchum as he drifted off to sleep.

And done, I hope you weren't expecting too much, this is only the prologue so it's not even really the first chapter yet, but still, constructive criticism will help me, I know how I want this story to end, and the basic way it will go, but I haven't gotten all the middle stuff worked out yet, and the fact that RWBY episodes are still coming out may affect the course of the story, we'll see what happens, review if you want to.