@Thunderbasilisk
About 50/50 him crashing through the roof will be a reoccurring driving force for the story
@sethelephant
I have Ash's team mostly planned out, but just like proper Unova there will be a large-ish supporting cast and you actually listed a handful of Pokemon they'll have
Now, onto the story!
"None of this makes sense." An older woman said, checking on the black haired boy that fell through their roof the other day. "A fall like that, he should be dead or at the very least a broken arm or leg or more, but it's just some scratches and this coma like state."
"When he wakes up he will be for what he did to my room!" The girl with long brown hair said.
"Rosa, I told you we would get it all replaced and fixed, just try and relax." The woman said.
"Great idea Mom, where should I go? Our one couch is being used by whoever this is, and oh yeah MY ROOM HAS A SKYLIGHT!" Rosa complained.
"Rosa, I understand you're angry but yelling at me does nothing about that. Why don't you go to the Pokemon Center and see how his Pokemon is recovering, the more we find out about them the better." Rosa's Mom reminded. "Just who are you and where did you come from?"
Meanwhile
"Mrs Ketchum, I assure you we have an APB out on your son and his Pikachu, if either one of them shows up at any Pokemon Center, Police Station or Gym from here to the Blueberry Academy we will know about it." An Officer Jenny said.
"But why hasn't he responded, it's been two days, do you think something has happened to him?" Delia asked still in a panic.
"Mrs Ketchum, I don't know, we're doing all that we can though." The Officer Jenny said.
"Delia, let's just head inside for a bit, and try to relax." Professor Oak said.
"My boys are missing! How am I supposed to relax right now?!" Delia asked angrily.
"I understand, but we can't stress ourselves over this all at once, what good are you to Ash if you worry yourself half to death?" Professor Oak said calmingly.
"Okay, yes, I understand." The Officer Jenny said, responding to a radio transmission. "Have them send back the answers as soon as they can."
"Is everything alright?" Professor Oak asked.
"Yes, maybe, one of our further out Pokemon Centers, most traditional communication is down right now, however they reported a heavily injured Pikachu in their care." The Officer Jenny said. "They will send back more information when they can."
"Pikachu are quite rare here in Unova, it's possible that it's Ash's Pikachu." Professor Oak said. "With any luck, Ash might have landed with him."
Back elsewhere
"Nurse Joy? I'm here to check on a Pokemon." Rosa said walking into the small Pokemon Center.
"Ahh Rosa, welcome back." The Nurse Joy said.
"Bwarp!" Lillipup barked from Rosa's arms.
"You too Lillipup." The Nurse Joy said. "Yes, we actually just got information about this Pikachu. I was hoping you might be able to answer some questions about it."
"Other than it and that boy destroying my room, I don't have many answers." Rosa said still angrily.
"Bwarp!" Lillipup barked in agreement.
"Yes, well the questions are about the boy he was with. Can you describe him to me?" Nurse Joy asked.
"Sure black hair, tan complexion, probably annoying and a jerk." Rosa began to rant.
"Rosa, this isn't like you, please we're trying to help him." Nurse Joy said.
"No one knows what I'm really like, thats why I'm here." Rosa said with a huff before sighing. "Fine, I don't know about this tall, maybe 15." Rosa said, putting her hand a bit above her. "Brown eyes, is this enough?"
"Yes, I'll send the information back to where they asked." The Nurse Joy said.
"Can I ask a question though?" Rosa asked.
"Of course." Nurse Joy said, looking at the girl.
"That Pokemon, you called it a Pikachu, but I've never seen one before, how do you know what it is?" Rosa asked curiously.
"I spent some time in Kanto before moving back here." The Nurse Joy said. "Pikachu aren't exactly common there either, but they are far more common in Kanto than they are here in Unova. They're an electric type too."
"Could it maybe have come from somewhere else?" Rosa asked.
"Pikachu are found all over the world, usually they are quite rare and stubborn Pokemon though." Nurse Joy said. "I wonder where this little guy came from."
"Well, thanks for the update Nurse Joy." Rosa said.
"Oh wait, Rosa one more question, has your mother given any update on the boy's condition?" Nurse Joy asked.
"Right, she said he's lucky to be alive and the condition he's in considering his fall." Rosa said. "Physically he's fine for the most part, just comatose."
"Thank you Rosa." Nurse Joy said.
A bit later, back with Delia and Professor Oak
"Alright, sorry about the delay, we haven't used our fax machine this much in a while." Officer Jenny said.
Authors Note
If you don't know what a fax machine is, I don't blame you, they're old even for me and I'm almost 30, yikes. They were effectively emails before emails were a thing, and are still used a bit, but not much any more. Back to the story!
"So, did they find him?" Delia asked.
"The boy found with the Pikachu matches the description of your son, and we will keep you both updated on all of that as we learn more." Officer Jenny said.
"See Delia, they're together, if I know Ash and Pikachu, as long as they're together, nothing can stop them." Professor Oak assured.
Elsewhere Elsewhere, in between dimensions
"Wow, you were not kidding about needing me here, what hit this one?" Trap Ash asked as they entered the domain of Pokemon Master Ash.
"Honestly, I was hoping you could tell me." Pokemon Master Ash asked, seeing the bubble looking at the Ash in a coma in Unova. "You're the only one who I've been in contact with who's also been to Unova so far."
"And you said he had just arrived when it happened?" Trap Ash asked.
"A few minutes or so, why?" Pokemon Master Ash asked.
"When Pikachu and I first got to Unova, we were attacked by a Pokemon called Zekrom, it hit Pikachu and drained him for a bit, but nothing like this happened to us back then." Trap Ash said. "Have you tried checking with Pinky to make sure he's still alive?"
"The portal shows him, so he's definitely still alive." Pokemon Master Ash said. "But whatever he did to survive that fall, it's got to be nearly on par with our aura abilities, possibly even greater."
"Keep us posted, if his world gets too risky, he might need backup." Trap Ash said, this is way off course even by our standards."
"Will do." Pokemon Master Ash said.
Authors Note
Real quick, no this is not a crossover, this is simply showing that the other Ash's are still in contact, and PM Ash is still watching over the multiverse