Real Quick, going to answer some questions here because I keep forgetting to do that.
@True Master
I'm not going to have Ash catch Meloetta, as fun as giving legendaries is, Ash already has his legendary for the story. I can't believe that is a thing in ALL of my stories now but it is.
@n.j
Why aren't Cilan and Iris in this story. Short version is Ash went to the wrong side of Unova. Long version, for most of my stories I like giving a new group where I don't have as much constraints on the characters. If I did Cilan and Iris there wouldn't be much extra I could do with them that isn't expected.
And in general as for shipping, there isn't any major ones. I won't stop you from thinking Ashxinsert character here, but there will be no blatant ship for this story. Don't worry the next one I promise will have at least one love triangle.
Now with those out of the way, ONTO THE STORY!
"So this is the inside of Reversal Mountain. Pretty cool." Ash joked, looking at the river of lava down below.
"Out of the way out of the way out of the way!" A young woman said, bumping into Ash.
"Solo!" Solosis exclaimed, catching both Ash and the woman before they fell into the gorge.
"Ash! Are you alright?" Rosa asked as Solosis set him and the other person down.
"Yeah, just give me a second to catch my breath. Thanks for the save Solosis." Ash said to the psychic type.
"And you, who are you thinking running through a cave is a good idea?!" Rosa exclaimed.
"Sorry, I tripped and have a bad habit of crashing into things to stop. It's usually not people though." The woman admitted. "I'm Bianca by the way."
"Ash." Ash said raising a hand slightly, as he readjusted his hat. "What are you even doing in here?"
"Oh I'm here on behalf of Professor Juniper." Bianca admitted. "She has me looking into a legend deep in the cave, I was supposed to meet an old friend of mine here though. I wonder where he is?"
"You know Professor Juniper?" Ash asked.
"Know her, I'm her assistant researcher, I even got my first Pokemon from her!" Bianca said excitedly. "Do you know her?"
"We know her sort of, we also know her father." Elliot pointed out.
"Bianca there you are, do you have any idea how long I've been waiting?" A familiar voice to Ash and Rosa said with a sigh walking over.
"Mr Cheren, what are you doing here?" Rosa asked.
"Ash, Rosa, I could ask the same thing, Reversal Mountain isn't quite on the beaten path." Cheren commented.
"Cheren you know these trainers?" Bianca asked.
"A little, Ash was actually my first challenger as a gym leader." Cheren pointed out. "How's that going by the way?"
"6 badges down." Ash said proudly.
"Hmm, perhaps we could use his assistance." Cheren said.
"Are you sure, this is could get dangerous." Bianca reminded.
"Danger is my middle name." Ash said.
"It's Richard." Rosa pointed out.
"Fine, then I have danger for breakfast!" Ash said.
"You had half a pop tart and a gogurt for breakfast." Elliot reminded.
"Point is I can help. Pikachu and I face danger all the time!" Ash argued.
"I don't actually have a counter for that." Rosa admitted.
"He did almost just fall into a lava river, how much more dangerous can it get than that?" Elliot asked.
"Yeah, about that." Bianca said sheepishly.
A bit of traveling downwards later
"Whose big idea was it to research closer to the lava." Rosa said, feeling the heat.
"Yeah, how much longer are we going to be down here?" Elliot asked, trying to stay away from the flow.
"You two could have stayed up there and waited for us." Ash reminded.
"Yeah, but if we run into trouble, we like our chances with you, a gym leader, and a professor's aide more than on our own." Elliot pointed out.
"Technically Cheren is a former Minor League champion." Bianca informed.
"Wait, you competed in a Pokemon League?!" Ash asked in shock.
"A few years ago, got all eight badges needed and ended up winning." Cheren admitted.
"So the team I faced for my badge, was that it?" Ash asked curiously.
"No, no, my league team doesn't get as much use nowadays, though I do have a few of them for this mission." Cheren admitted.
"See guys we have this in the bag, a minor league champion, a professors aide, and me, with my…42 badges and 7 frontier symbols." Ash said thinking for a moment.
"You know I have to wonder, what exactly are you researching that needs both of you and could warrant the idea of adding more help?" Elliot asked. "Surely most of the challenges in this cave would be easy enough for the two of you to handle on own."
"Heatran." Ash said, noticing markings on the wall. "You think there's a Heatran down here."
"You recognize it's shell's design as well." Bianca said surprised.
"Have you even encountered a Heatran?" Elliot questioned.
"Twice. Once was in the past though." Ash said.
"Well yes that's how encounters tend to work." Elliot said.
"No, I mean, never mind, it would take over an hour and a half for me to explain that adventure." Ash sighed.
"Ash is right about the Heatran possibility, which is why we need to be prepared. Every legendary must be handled with caution, and when it comes to them there is no such thing as over prepared." Cheren said, as the group reached a pinpoint.
"You think it's in there?" Rosa asked.
"One way to find out." Ash said, walking into the room, seeing the sides filled with lava.
"Hmm, I was certain that Heatran would be in here." Bianca commented.
"It's possible that there was one here at a time but it's not here right now." Elliot remarked. "I would have loved to see a battle against one."
"You know as long as we're here, and you do have some of your champion Pokemon, how about a quick one v one?" Ash asked.
"Well I suppose my starter could use a good battle." Cheren commented.
"Alright then. Starter for a starter. Pikachu I choose you!" Ash exclaimed.
"Serperior, let's go!" Cheren called out.
"Pikachu use Quick Attack!"
"Serperior use Coil!"
Cheren's Serperior moved with incredible speeds, wrapping Pikachu up as it began to squeeze.
"Pikachu use Thunderbolt!"
Pikachu let loose a burst of electricity with enough force to loosen Serperior's grip and free himself.
"Pikachu use Iron Tail!"
"Serperior use Dragon Tail!"
Pikachu leapt forward, swinging his tail at Serperior as it was swiftly blocked, locked, and knocked back by Serperior's own tail/lower portion.
Authors note
Seriously, where does a snakes body end and their tail begin? Quick google search says about to of their body, but I don't know.
"Pikachu get up and use Charge Beam!"
Pikachu hopped back up, skidding to a stop as static began forming in his cheeks.
"Serperior use Leaf Storm!"
Serperior sent out a flurry of leaves at Pikachu, striking the electric type multiple times and blocking his Charge Beam.
"Now use Leaf Blade!"
"Pikachu dodge it!" Ash called out.
Pikachu leapt out of the way, only for his tail to be struck once more by Serperior's tail, pinning the electric type to the ground.
"And we'll call the match here." Cheren said. "Honestly Ash you show potential and if we were in a properly sized arena, I'm sure Pikachu could give Serperior a run for his money."
"Thanks Cheren, and hey next time we meet, I want a real battle." Ash said confidently. "No gym team, no one on one. You and me giving it our all in a full battle."
"Well then Ash, I look forward to the challenge and you know where you can find me." Cheren said with a smile.
Third and Final Author Note for this chapter
Yes Cheren and Bianca! I figured since Bianca had Emboar in the anime, logically that would give Cheren Serperior. That's about it for now.