AN: This story may/may not be a oneshot, depending on my mood.
!Edit!: This chapter has been revised and changed because I gave it some thought and decided my style and ideas were particularly weird and out of place.
It was a beautiful day in Sinnoh, with the morning crisp air blowing in the faces of three trainers and a Pikachu. The Pikachu was riding on the shoulders of a spiky-haired, particularly ambitious trainer named Ash. Along him and his companion were two other trainers: Dawn (a girl with the dream of becoming the top Coordinator), and Brock (a tan man who dreams of becoming the world's best Pokèmon breeder). They were traveling to Route 209 to get to Hearthome City to see Gym Leader Fantina for Ash's next gym battle.
"Alright! I can't wait for the next gym battle! You ready Pikachu?" asked an excited Ash. Pikachu nodded in response.
"I just know you'll win, Ash. You and your Pokèmon have been training really hard," Dawn encouraged.
"I couldn't agree more. Leader Fantina may have strong Ghost-type Pokèmon, but you and your Pokèmon will be able to pull off a win," Brock added.
"Yeah!" Ash said determined, and began to sprint through Route 209 to Hearthome, nearly causing Pikachu to lose balance on Ash's shoulders.
"…Guess we should follow him," Dawn sighed, and she and Brock went to chase after the excited soon-to-be Pokèmon Master.
As Ash was nearing the gates, he spotted someone up ahead. Being the nice guy he is, he decided to speak to the person. When he got closer, however, he found that the person was a woman and was working on some sort of potion. He suddenly remembered her to be the Pokèwitch, Lily. Lily turned around, sensing that someone was nearby, and was surprised to see Ash again.
"Hm? Ash, Pikachu, is that you? Fancy meeting you two here," said the Pokèwitch with a British accent.
"Hey Lily. It's been a while. What are you working on now?" Ash asked.
"Oh, this? It's a potion that transforms whoever drinks it into the Pokèmon of their choice," she responded. "But I don't think it's temporary. If drunken, I do believe you will remain that way forever. It's possible that it might wear off, but I just don't know. The spell here seems a bit cryptic. No one knows for certain." At this moment, Dawn and Brock caught up with Ash and Pikachu.
"Hm? Who's that?" Dawn asked.
"That's Lily, the Pokèwitch. We met her one time in Johto. With Ash and Pikachu's assistance, she cast a spell that was supposed to help Ash better understand Pikachu, but it…backfired and turned him into one," Brock explained.
"Oh…At least the spell wore off." She paused for a moment and said, "Wow, that must've been really cool! Ash, I didn't know you was once a Pikachu! And Lily, I didn't know you transformed him! That sounds so cool!"
"Lily, this is Dawn. And you remember Brock, right?" Ash said as he introduced the duo.
"Nice to meet you, Dawn. And nice to see you again, Brock," the Pokèwitch responded.
"So, what are you working on?" Brock asked.
"A transforming potion," Ash replied before Lily could answer. Instantly, Dawn looked closer at the potion, sparking a warning.
"Don't get too close! I don't know if the potion's effects are temporary or permanent. One touch could be all you need." Lily warned.
"Why? What'll it do?"
"It will transform you into a Pokèmon of your choice. I'm confident that this time, the spell will NOT backfire," responded Lily. "It's not tested yet." At this, while Brock, Dawn, and Lily continued talking, Ash walked towards the potion and began to think about what could happen if he drank it. Pikachu glanced at her trainer and saw the look on his face.
"Pi, Pikachu? (Ash, what's wrong?)" she asked her trainer.
"Oh, I was just thinking about that potion," was his quiet response. He understood what Pikachu was trying to say.
" Pi, ka pika (Are you going to drink it?)"
"If I do change, I'm not gonna freak out like I did last time because it'll only last a day. Besides, it hasn't been tested yet, so I don't think Lily would mind if I tried it out for her."
'One touch could be all you need.' Lily's words rang inside his mind. He touched the surface of the bubbling liquid and reeled back, expecting something to happen. Strangely, nothing happened. 'That's weird,' he thought. He decided to take a small sip of it against his better judgment drunk it. Not feeling any sudden effects, he assumed that it would be active the next day. Before anyone could see him, he went back to the group to tell Lily good bye.
"Well, it was nice seeing you again, but me and Pikachu should get some rest in Hearthome City. It's starting to get late," Ash stated, waiting for the right moment to speak.
"Oh, you're right Ash. The sun's going down. Well, I better be off. I completely lost track of time. I'll see you four another time, perhaps?" With that, Lily cast a Teleport spell to completely disappear.
"…That's amazing. Like a real coordinator," Dawn said, clearly amazed.
"It looks like it's too late to go challenge Fantina. Maybe you could do it tomorrow, Ash," Brock suggested. Ash nodded in agreement.
The group decided that the Pokèmon center would be the best place to spend the night. Upon going through the doors, Brock instantly began to flirt with Nurse Joy until he was, of course, neutralized and dragged away by his chaperone, Croagunk.
"Would you like me to heal your Pokèmon? You can also spend the night here," Nurse Joy stated. All three trainers nodded and handed over their Pokèmon. After a few minutes, they got their Pokèmon back and went upstairs to the guest rooms. Brock and Dawn slept in one room while Ash and Pikachu slept in the other room. The two began to chat, lying on the bed and gazing into the starry sky.
"For some reason, I don't think the potion even works. She may have said it would work, but I just don't really know now," Ash said, skeptical about its effects.
"Pi pika chu (I'm not so sure. It might work)," Pikachu responded. The pair quickly fell asleep from exhaustion (Pikachu sleeping om Ash's chest), but had they been awake a little longer, they would have noticed the potion beginning to take effect. Ash's clothes began to vanish, being replaced with yellow fur everywhere except part of his back, which gained brown fur. He grew a Pikachu tail and ears, and began shrinking to the size of a Pikachu. His eyes remained the same, although his hair changed color. His hat was the only article of clothing that remained.
Ash had became Ashachu again.