Ash in Mystery Dungeon 1
There was a young boy named Ash Ketchum who was fast asleep, but when he woke up, he found himself in some strange colorful void. Where was he? What was going on?
The dreamer wakes... Choose your destiny...
Ash looked around, where was that voice coming from? "My... destiny? What destiny? Who are you?" He called out as he looked around, he couldn't even see himself. What was happening here? What kind of dream was this? The voice spoke again.
You will meet me again in time... In the distant future. First... what is your name?
"A-Ash... Ash Ketchum of Pallet Town. I'm the son of Delia Ketchum." He answered, was this some sort of bizarre questionnaire?
Do you care for your friends and Pokemon? Or you do care about yourself?
"I care for all of these people and Pokemon! How could I be selfish? Yeah, I had a few moments... But in the end, I would be close with my friends and Pokemon." He answered truthfully and then wondered... what would happen to his friends and Pokemon now? Would they be okay?
You are kind and caring, and have a fiery determination resonating inside of you. Despite your age, you show remarkable maturity!
Ash blushes at that and could imagine himself scratching his neck nervously. "Eeheh... I'm not special. I'm just a boy."
Regardless... You are worthy to take this task. In this world, it is in mortal danger. You will travel to this world and solve it's problem. Once that is done... your task will be finished and you will return from whence you came.
"Wait, what?! Slow down! What world? What danger? I can't go back home until I'm done!? Who even are you Voice?! Answer-!" All of a sudden, he felt light headed and his vision was starting to get blurry. "Wh... wha...? M-my... head..."
Go forth, Chosen One... Boy chosen by the Legends and blessed by Ho-Oh's Rainbow... Go forth... and... s........ world.......

When Ash woke up, he groaned as he felt the soft grass and a cool breeze. He opened his eyes and saw the clear blue skies with the occasional clouds passing by and the bright sun overhead. "My head... what happened...? Was it all a dream...?" He said to himself and went to rub his eyes, but stopped as he saw... he had no skin, but fur! And it was a paw!
He was now wide awake and screamed in surprise. "AAH! What the hell?! Wh-why do I...?!" He bolted up and became unsteady and collapsed to his knees. He had blue and black fur, some spike nubs on the front of his paws, and felt the grass on his pawpads. He crawled over and found a small pond. He gasps and grew wide eyed once he stood up.
"I-I-I... I'm... I'm... a... POKEMON?!?! A Riolu!?" He screamed so loud, he could have sworn some Bird Pokemon flew away from the loud sound. He felt his cheeks and it confirmed it once he saw the reflection matched, he looked down and saw he was without any clothes. Except for his hat. He even had a ballsack showing and covered himself up and blushes.
That voice... it said it would bring him to a world in danger... was this that world? And he was turned into a Pokemon for this purpose? "Where am I...? What region is this? Wait, is it even a region?" He had so many questions, but nobody to tell him the answers, then, he felt something poking out of his sheath and blushes even more. His cock poked out.
"N-no... B-but I wasn't... my new body... No... I... I have..." This was too much and he just burst into tears. He collapsed on his knees and bawled his eyes out. "I WANNA GO HOME...! I WANNA GO HOME...! I... I wanna..." He covered his face with his paws and sobbed. "I wanna go home... Mom... Pikachu... What am I supposed to do...?" Ash was in the middle of some clearing he didn't know, in a place he was unfamiliar with, and most likely, with Pokemon who wanted to beat the shit out of him.
"What am I supposed to do...???" Ash wiped away his tears and shakily stood back up. Crying wasn't going to help, nor acting like a brat. He had to take action. He saw a trail leading to somewhere, it beats sitting here feeling sorry for himself. He followed the dirt trail and saw that the forest shifted and got distorted, once he looked back, the trail was gone.
"What...? What happened to the entrance?" Ash's ears twitched once he heard some movement and the rustling of bushes and trees. He wasn't alone. There were others here, most likely Wild Pokemon. That's when another horrible thought came in. He had no clue how to fight. What did a Riolu have?
They had Aura powers... but they wouldn't be developed until later, so that was out. All he could do... was basically tackle and growl. Ash gulped and made his way into the labyrinth of a forest. He heard more rustling, but couldn't figure out where they were coming from. He was then tackled on the ground and landed with a loud thud. "Gaah! Ow! L-let go!"
Ash could see from the corner of his eye something purple and spiky. A male Nidoran, who grins and chuckles. He then felt something big and thick on his asscheeks and paled. "Ah..." There was no mistaking it, he could feel the Nidoran's penis, hotdogging him and letting out some groans. 
"Mmhf... such a plump ass for a Riolu... hehehe... lucky me~" He said and growled in lust, Ash tried to get away, but he could feel the Nidoran pinning him down good. "P-please... I-I'm a boy! I'm not a girl! Wouldn't you like a girl for this?!" He said, hoping this would gain him a chance to escape, but no dice. The Nidoran laughs and feels the tip poking his entrance.
"Nope~ You're way better than a girl!~ And I'm gonna claim you!" He then thrusts inside, making the human turned Riolu's eyes widened like saucers and screamed loudly for anyone to hear. "AAAAAAAAHHHHH!!! NOOOOOO!!!" The Nidoran held Ash's waist and started pounding his tight ass, a bit of blood leaking out as he was unprepared.
"Mmhf... so fuckin' tight...! This your first taking anal, bitch? Must be lucky!~" Ash just screamed some more, he felt a burning pain in his backside and tears trailed down his cheeks. "Take it out! It hurts so much! HELP ME! I'M BEING RAPED!!" The Nidoran growled and slamed Ash's head onto the ground, making him bruised and have a black eye. "Shut up, whore! You don't get to talk while I fuck you, faggot!"
Ash whimpers as he was called derogatory words. Why was this Pokemon so cruel to him? Why was he being raped? All he could do was sob and whimper, unless he incurred more of the Wild Pokemon's wrath. "Mmhfh... such a tight ass, for a bitch boy~ Strolling around with that thick bubblebutt~" Ash blushes, did he really have such a feminine appearance? Although, his voice didn't help much either.
He also felt his cock poking out of his sheath and getting hard. Was he turned on by this?! This was horrible! "Mmhf... fuck... I'm gonna cum!" Ash whimpers again as he felt the Posion Pokemon's thrust going harder and rougher until he slammed balls deep and unloads his semen. "AAAAHHH!!! NOOO!!!" Ash screams as he felt the warm liquid inside him.
The Nidoran pulls out and stains Ash's back, as the Riolu boy pants and sobs some more. He was the turned over on his back as he was stricken with fear, the Nidoran plunges his cock inside again as the Riolu screams in agony. "Mmmf... such a cute face too... shame you had to be disobedient. Now... stroke yourself." The Nidoran ordered.
"S-stroke... myself...???" Ash stuttered, what was he talking about? He then heard him growl and glare at him. "Grab your cock and jerk off, dumb fag!" Ash let out a whine and quickly grabbed his shaft with his paw and moved it up and down, that seemed to appease the Wild Pokemon who groans as he continued pounding away.
It felt so weird... was this what masturbation was like? And the pain in his ass still hurts. "M-my... butt hurts..." Ash said quietly, but the Nidoran ignored him and roughly fucked the Riolu, the sound of whimpering and moaning could be heard in the forest. "Mmhhf... here comes another load bitch!~" The Nidoran came and filled up the Riolu, at the same time Ash came and stained his chest. He collapsed and was panting and breathing heavily.
The Nidoran pulls out and stains Ash's face and chuckles. "Hehehe... thanks for the stress relief, faggot. Happy travels~" He then wandered off, leaving Ash lying in a mixture of fluids and cum to process what just happened. He then felt so tired as cum and blood leaked out of his abused hole. "H-help... me... this... this is hell... I... I wanna die..."
Ash then welcomed the darkness and passed out, but before he did, he could faintly hear some footsteps and someone gasping. And that was it. What will happen next? Who knows? Only time will tell once Ash travels into this strange, alien world where Pokemon act on their sexual urges.
THE END