This, like "A Chess Game Gone Wrong", just popped into my head and I couldn't not write it.
"Hi. My name's Corrin. I'm the protagonist of Fire Emblem: Fates, which the writer, Hammershlag, hasn't played yet," the white-haired man smiled. Wait, is this a first-person fic or a third-person fic?
"Shut up and narrate," the author, Hammershlag, said.
"Hey, shouldn't your name be HammerSCHLAG? You know, since Hammerschlag is German for 'Hammer Strike' and Hammershlag doesn't mean anything?" Gunter, the resident Jagen said.
"Hey, narrator! I'm an Oifey in Birthright!"
"No-one cares, old man. Now someone fetch me a chimichanga," Deadpool, the resident third-party character–
"Shut up Narrator, everyone knows who the fuck I am." Don't interrupt me while I'm narrating you son of a bitch!
"Hey, language! I want to keep a T-rating here and if I'm going by MPAA rules I'm only allowed one F-bomb." Hammershlag snapped.
"No-one respectable calls them 'f-bombs', you f**king jack– wait, did you just f**king censor me?! You stupid–"
"I'm the author. I can do whatever the eff I want."
"You're not British; stop using British mannerisms."
"I don't care what bloody ethnicity I am you wanker! I'll use whatever mannerisms I want!"
"Well screw you too. And when you're done with that, you can give me some chimichangas," the Caption Box that represents Deadpool's–
"Why do you do that?" Do what?
"Capitalize things that don't need to be capitalized." Ask Hammershlag; I'm just the narrator.
"EVERYONE SHUT UP. I WANT TO TELL THIS STORY!" the writer screamed.
"Technically, you're the one making us rebel,"
"Well, you're all part of my subconscious, so… SHUT UP, SUBCONSCIOUS CHARACTERS!"
"I think he's lost his mind," Gunter folded his arms.
"Master Corrin?" Felicia walked in.
"Really? ANOTHER Corrin x Felicia fic?" Deadpool rolled his eyes. Just let me tell the damn story like I'm being paid to.
"Fine. Go on, Felicia."
"Umm… okay…" the maid hesitated, "there are a lot of Earthquakes outside… I think you're breaking the fourth wall too much. Can we please try to stay in character?"
"What fun would that be?" Deadpool smiled.
"Wade's right. I'm writing this for fun, so let's have some," Hammershlag smiled.
"Why thank you, M–"
"HEY! Do NOT call me by my real name! I don't need it on the damn internet!" the writer put his hands on his hips. Wait, how can you put your hands on your hips while you're typing."
"That's not important."
"I beg to disagree," Deadpool said.
"Well you can go straight to hell."
"Okay," Hammershlag smiled as we wrote Deadpool as being teleported to hell. Unfortunately for the writer, Deadpool reappeared in Corrin's castle (the setting) a mere moment later.
"Teleportation Belt + Infinity Stone + Having a relationship with Death = control over whether or not I go to hell."
"Or up your mother's–" the Caption Box started, but I, being the almighty narrator, decided to cut him off: Hey, can we try to keep it clean?
"I'm afraid that may be impossible," Gunter scratched the back of his head.
"No it's not. I'm the writer, so I'm keeping it clean."
"Oh yeah, watch this: [censored]. Wait, what the f**k?"
"I'm the writer. I can censor whatever I want."
"I thought this story was about me…" Corrin muttered.
"It was, but we've kind of taken over," the Caption Box chuckled.
"Hey guys, sorry to bother you," a random castle guard in a red shirt walked in. Really? We're putting in classic Star Trek references that no-one will understand?
"I'm sure SOMEONE out there understands them. Leave a comment if you do! Or if you don't…" You're a real attention whore, aren't you?
"Err, there's a portal outside, and it's spewing–" the guard was cut off by a spear going through his head… a spear wielded by a mo…
"Say it." No.
"SAY IT!" I'm not referencing FE7.
"Fine. Just call it a Risen something." That's better. As I was saying, the guard was cut off by a spear going through his head… a spear wielded by a Risen revenant.
"Hey! That was a great movie!" Deadpool smiled. Not THAT Revenant, dumbass. I mean the cheap knock-offs of the monsters from FE8.
"Oh. I don't remember those."
"No-one does," Gunter said.
"Why do the red shirts always die?" Felicia asked
"That's the trope. Deal with it," Hammershlag shrugged and put on those cliché black sunglasses.
"Guys, the portal's getting bigger…" another red shirt walked in… and was promptly killed.
"Where'd it come from?" Corrin frowned.
"A plot hole," Deadpool suggested, "or maybe, the portal itself IS a plot hole!" That's a worse idea than everything Hammershlag put in Tale 9B of FE:CSR, which we all know was a complete mess.
"Hey! I already told you I'm going to re-write it!" A rewrite of a rewrite, huh?
"REWRITECEPTION!" everyone screamed at the same time, including me.
"That meme is really old," Hammershlag groaned.
"Old and stale are two different things," Gunter grunted.
"Says the Jagen."
"You f**k off. AND STOP CENSORING EVERYTHING!" Corrin shouted.
"OOC, much?" the Caption Box teased.
"This is a fourth-wall breaking fic. Canon is irrelevant," the writer said.
"Guys, I think I see something in the portal!" Felicia exclaimed.
"Five walls! The first four are already broken, and the fifth one's cracking." Wait a minute… do you guys know what this means?"
"Oh my God, we've broken the fourth wall so thoroughly, we're about to break a fifth one!" Deadpool cheered.
"I wonder what that wall does…" Corrin scratched his chin.
"Cormag Ravenstaff asked the same thing after I reviewed his fourth wall breaking fic, 'Over The River And Through A Plot Hole'…" Hammershlag shrugged.
"Well, there's only one way to find out!" Deadpool smiled. At that point, everyone present made as many fourth wall jokes as they could think of, and the so-called fifth wall continued to crack. Eventually it broke and– hey, why are all the colors inverted?
"And why are we all losing form?"
"Oh no! We're all disappearing!"
"That buzzing noise is driving me nuts!"
"Guys, I think we may have taken the fourth wall jokes a little too fa–"
The end, I guess? Well, there's the answer to what happens if you break the fourth wall too much – the universe ceases to exist.
ULD Prologue 2 is next, then FE:CSR Tale 9x Chapter 4.