Idea from: BlazingBluex7
It
It wasn't every day that you could watch Ash running around, chasing a little yellow rat around the hotel room while Dawn and Brock watched with a cool, calm disinterest, casually flipping cards over as they played the card game War (because, really, it's the only card game you can play for hours and never get bored). Ash had been doing this (with breaks not included) for about two and a half hours. It had all started innocently enough, but had developed into something crazy and, Brock and Dawn being sensible folk, had settled down about thirty minutes in to begin their card game.
"There's two fives again," Brock sighed, wishing the card game would end already.
"Go fish," Dawn muttered absently.
"Will do." And he did go fish, through her card pile, easily shuffling through while she lost focus with untamable boredom and stared at the ceiling, dreaming that it would all soon end. It wasn't long before she was out of aces and kings and he snapped her back into focus with an attempt at not sounding smug (but failing), "Come on, let's finish the game. Ash isn't going to finish any time soon, but we might be."
Dawn groaned. "Ash, I'm sorry I asked. I don't really care. Why don't you just ask Joy next time we get in a center?"
"Because!"
"Because why?" she argued.
"Well…because!" he spluttered, once again pouncing on his pokémon who scooted away.
The little thing leapt up onto the bed, and proceeded to charge whenever Ash dared to approach, and wouldn't stop until he had backed up to a respectable distance. Ash plopped on the floor and crossed his arms, locked in a deadly stalemate with his pokémon. How long had he owned it and never bothered to check? By now he should know, especially since he was getting to the age where the daycare centers could be quite lucrative if he dared to try.
"Gees, Ash, it shouldn't be that hard to tell. There should be some kind of-"
"Not in Kanto," Brock sighed. "Not in the 'pure' Kanto. Pokémon have been released from other regions recently, but our stuck up pokémon almost always refuse to breed and chase them off. So, those pokémon start their own little tribes and we just have to sit back and let them do it. They aren't nearly as strong, but it makes for great conversation when you manage to catch a purebred. They're pretty difficult to befriend, but once they do they're very loyal."
"Someone's not being to loyal now," Ash shot up.
(Golly gee, I don't want my trainer violating me in so many ways it's not funny and refuse to let him lift my tail just so he could find out what he could have found out by calling the Professor or setting me up with some hunk. I'm a girl, dammit. Purebred Kanto beast, no dent in tail. We're pure, strong, and we don't breed with your weaklings! We bury ourselves in the ground to get stronger and we spit on humans! You're lucky I took a liking to you, and you're not a Pikachu, but you're my horde now.)
"Ash, what'd she say?" Dawn asked eagerly.
Ash's face contorted with stupidity only he himself could muster. Finally, he took a deep breath in and out and quite honestly declared. "I dunno, but I'm pretty sure I can't look under its tail to figure out if it's a girl or boy, so there's only one way to settle this."
He stood up straight, looked the rat dead in the eye and bravely stated, "Hey there, fella."
The electricity was coursing through him in no time, and soon he landed flat on his face, moaning and twitching. He was exhausted, poor simpleton, form running and trying to see under his pokémon's tail. He fell asleep there on the floor, snoring loudly and dreaming about a world where genders didn't matter, or were engraved on forehead's so he could tell them apart and not get horribly, horribly injured.
"…So Pikachu's a girl, even if there's not a dent in her tail?"
"Kanto bred, no difference between them, like I said. At least now the mystery is put to rest."
Moral of the Story: Pokémon, except for certain "special" pokémon, have genders. Use them. And, if you don't use the commonly accepted gender, have a good excuse.
No, Pikachu being female is obviously not canon, but I really don't care. I explained it, see? You can rape canon if you can explain it. It's sort of like having a good lawyer in a crime you obviously did, no names mentioned. Hope you enjoyed!