Sho, the Electric Trainer

One day...
The gang was having lunch, when suddenly Piplup dropped some of it's food and it rolled away. Piplup chased after it, but a Pichu found it and ate it. This made Piplup angry. Pikachu stepped in to stop Piplup. Seeing Pikachu made Pichu call out. It seems Pichu had a trainer, a boy about a year older than Dawn.
"Good work Pichu, you found a Pikachu." The trainer said.
Just then Ash and Dawn came up to them.
"What did I say about you getting too far from us?" Dawn scolded Pikachu.
"Back off all of you. That Pikachu is mine to catch." The trainer said.
"What?" Ash exclaimed. 
Before he could say anything else the boy sent out a Raichu.
"Iron Tail." He ordered.
"Pikachu, Iron Tail as well." Ash ordered and the two attacks collided. 
"That Pikachu is no untamed Pokemon with that power." The boy said.
"Of course not!" Ash shouted. "Pikachu is my Pokemon! Now what do you think you're doing attacking him!"
The boy's name was Sho and he was a electric type Pokemon trainer. He wanted a Pikachu because he wanted a full power evolution set of the Pichu line. He had Pichu and Raichu, he just needed a Pikachu. Sho offered to trade Ash Pikachu for a Mareep, Magneton or Magnemite, but he refused. He wasn't going to give Pikachu up for any other Pokemon, besides he already had Ampharos and Magnezone. 
"If you don't want to trade, let's do this." Sho said. "You and I will have a battle, my Raichu vs your Pikachu. If I win Pikachu is mine." 
"What?!" Dawn gasped.
She didn't like the sound of this. 
"Very well." Ash said. "But if I win I keep Pikachu and you go find your own Pikachu."
Sho agreed to the terms.
Ash and Sho got ready to battle.
"Brock, Tomo I don't like this." Dawn admitted to the others. "Especially since Ash will have to give Pikachu to Sho if he loses."
"There's nothing to worry about." Brock told her. "They've battled electric type Pokemon before, including Raichu. Ash knows what to do when Pikachu faces Raichu."
Dawn hoped that Ash knew what to do. Unbeknownst to the gang, somebody else was also going to watch the battle. It was Paul. He was in the area and just witnessed Sho wanting to battle Ash for his Pikachu. He was going to see what Pikachu did against Raichu.
"Swift." Ash told Pikachu.
Multiple white stars hit Raichu.
"Not bad." Sho smirked. "But check this. Raichu, use your Thunderbolt."
"Oh no." Dawn said, worried.
She figured that Raichu's Thunderbolt attack would be more powerful than Pikachu's. But Ash wasn't worried.
"Pikachu, use your tail." He said.
Pikachu made his tail glow like he was about to use Iron Tail and he didn't take a lot of damage when Raichu's Thunderbolt hit him.
"What the?" Sho gasped.
He never saw anything like that before. Dawn was surprised with what happened too.
"That Dawn was a trick Ash learned in Fortree City in the Hoenn Region." Brock explained. "A Pelipper used Steel Wing when Ash's Manectric used Thunderbolt on it. But the Steel Wing acted as a lightning rod and Pelipper didn't take a lot of damage." 
Dawn wondered what else Ash's Pikachu could do. 
"Alright then Raichu, show that Pikachu your Slam attack." Sho said.
Raichu charged towards Pikachu to slam him with it's head. 
"Jump Pikachu." Ash said.
Pikachu used his tail as a springboard to jump out of the way before Raichu could hit him.
"Wow, look at that." Dawn said.
To Dawn, it looked like Pikachu used Bounce. 
"Okay Pikachu, it's time for Hidden Power." Ash said.
Pikachu fired a Hidden Power attack and it hit Raichu. Because Pikachu's Hidden Power was ground, it was super-effective against Raichu. Sho wasn't giving up though.
"Raichu, Thunder." He told him.
"Pikachu, use Protect." Ash said.
Pikachu protected himself from Thunder.
"See how you deal with this. Raichu, Hyper Beam." Sho said.
Raichu fired a Hyper Beam, but Pikachu used Dig to avoid it. 
"Excuse me." Dawn said. "But this battle is scaring me."
"Like I said, Pikachu and Ash know exactly how to deal with Raichu." Brock said. "And you better keep watching this because there may be times Piplup battles a Empoleon again in the future." 
Dawn remembered Piplup battling Empoleon in Alamos Town, but it wasn't as intense as this. Since Raichu used Hyper Beam, it had to recharge before unleashing another attack.
"Okay Pikachu, it's time to let Raichu have it." Ash said.
Pikachu came out of the ground and as quick as a flash he wrapped his tail around Raichu's tail.
"Do it Pikachu." Ash said.
Pikachu spun Raichu around and around by the tail then slammed Raichu hard on the ground. Sho was surprised by what Pikachu just did; he had never seen a Pikachu do that before.
"How the hell did your Pikachu do that?" He demanded.
"It's thanks to all the training and battles Pikachu and I have undergone together while traveling." Ash said.
"Pikachu, Volt Tackle." He ordered.
"Raichu, you do the same thing." Sho ordered.
The two electric type Pokemon collided with each other, causing an explosion and they were both blown back. Pikachu and Raichu were still standing though.
"Raichu, end this now with Hyper Beam." Sho said.
Raichu fired another Hyper Beam, but Pikachu dodged the attack before it could hit him.
"Pikachu, Hidden Power." Ash ordered.
Raichu was hit by the attack and was starting to become exhausted.
"Use Iron Tail." He said.
Pikachu charged towards Raichu and it charged at Pikachu to use Iron Tail as well. Pikachu jumped up to dodge Raichu and struck it with Iron Tail, then slammed into it. Raichu wasn't able to stand anymore and fainted. Ash won the battle, so he was going to keep Pikachu. Sho and his Pichu couldn't believe Raichu lost to a Pikachu.
After the battle everyone headed to the Pokemon Center and Pikachu and Raichu were healed by Nurse Joy. Sho spoke to Ash.
"With all the power that Pikachu had, I can't believe you didn't evolve it into Raichu. I mean, it will be more powerful than it already is after evolving it." 
"My Pikachu doesn't want to evolve, so I respect his decision." Ash said. "There are things Pikachu can do that Raichu can't. The traveling we did taught us a lot of things. And we picked up many battling styles based on what you saw during our battle. When you get your own Pikachu and train it, you'll understand what I mean." 
Sho could see that he was defeated; not just by the battle, but by his words.
After Pikachu and Raichu were well again, Sho left with his Pokemon to look for Pikachu and the gang headed to Pastoria City.
What they didn't know was Paul had been watching the battle and followed them back to the Pokemon Center. He thought it was pathetic that Pikachu didn't want to evolve, but he was impressed by how well it did battling Raichu. Then he headed to his next destination.