A/N: This is set in the same universe as the Jean and Armin being childish adults AU.
"You have got to be joking," Jean said. He'd just come home from a long day of work – and by long he meant he had to share a desk with fucking Eren of all people and the shit just had to rub it in his face that he'd been smart enough to order the new Play Station 4 and was well on his way to beating the new Call of Duty, while Jean, who quite liked braving the wilds of Black Friday, had planned on getting his system the fun and cool way, only to come up with nothing. So long story short, Jean wanted to strangle Eren, but since he couldn't do that without upsetting Armin, he had to clench his teeth and bear it.
Exhausted, his plan upon arriving home was to kick his shoes off, collapse on the couch, and whine until he got a sympathy blow job or at least cuddles of the naked variety. But that plan flew out the window when he walked into the house to see the living room thrashed, coffee table shoved against the furthest wall, couch devoid of cushions and lying face down, and a whole lot of sheets and blankets haphazardly thrown everywhere.
"Oh good, you're home!" Armin popped out from under the couch, donned in a light brown jumper and sweats, hair a mess – probably from squeezing himself between the space he'd created between the couch and the floor when he had, apparently, intentionally flipped it over.
"Yeah…" Jean answered, unsure, "What are you doing?"
"I'm making a blanket fort," was Armin's reply, as if it were the most obvious thing in the world – as if it were a normal occurrence for him to demolish their den.
"Oh. Cool," Jean guessed it was cool, except he'd been looking forward to using the couch for more, ah… physical purposes, and now it seemed he wouldn't be, "Why?"
"Do I need a reason?" Armin asked – fiddling with blankets. Jean noticed what looked to be folded up blueprints sticking out of the pocket of Armin's jumper – which meant this wasn't a spontaneous decision and rather Armin had been planning this for a while now. Christ, he was too cute. Who made blue prints for a blanket fort?
Jean chuckled, "Guess not. Need help?"
It was apparently what Armin had been waiting for, as he perked up before darting to the kitchen and returning with adhesive wall hangers and thin – but knowing Armin, heavy duty – rope.
He whipped the aforementioned blue prints from out of his pocket, before shoving all the items into Jean's arms.
"I marked all the places where you need to stick those hooks, but please refer to these drawings just in case, and I also included instructions explaining how to properly tie a square knot. I cannot stress how important it is that you use that knot – the others won't hold properly. Also, I attached eyelets onto the corners and ends of the sheets we will be using for the ceiling portion of the fort, that way we can loop the rope through there rather than trying to do a sheet knot. I'll hand the sheets to you as you go – it's impertinent that you use the right sized sheet. I'll hold the other end until you get it tied up as well so it'll be easier on you."
Jean blinked, trying to comprehend all the information Armin had literally just thrown at him, "Uh?"
"Jean!" Armin said in a no-nonsense tone, "Please pay attention, I can't do this without you."
Jean sighed heavily through his nose – Armin was giving him the look. The look being this cute little pout he did whenever he was mildly irritated and really wanted to do something he was excited about. His hands were on his hips and his lips were pursed and even though he was doing his best to scold Jean and guilt him into helping, the blond's eyes were still glimmering with barely concealed excitement, and it always made Jean smile like an idiot because seriously, how old was Armin? How could he still look so cute?
"Sorry, sorry. I was listening. And, I will remind you that I got all my badges when I was in the boy scouts so I don't need your silly instructions on how to tie a square not."
"Oh really?" Armin asked, clearly looking skeptical, "Because if I remember correctly, we were in the same group and your tying skills were so bad, that they even named that god awful knot you always seemed to tie after you."
Jean sputtered in embarrassment, "You're just jealous I was ingenious enough to come up with a knot never before seen!"
"Yeah, I'm super jealous that they are teaching the Kirschstein knot as the what-not-to do knot to kids these days."
Jean had the decency to look embarrassed, "You know they were just kidding right? They aren't really doing that?"
"That's not what Hanji says," was Armin's sly remark, before he was smacking Jean on the ass, "Enough talk though. Let's get to work cowboy!"
"Don't call me that!" Jean griped, but still got to work on the fort anyway.
Roughly an hour later, Jean was lying flat on his back on a pile of quilts and fleece blankets, catching his breath and mentally congratulating himself on a job well done. He had to admit, it looked pretty damn awesome. Sure it looked childish as hell, and with all the time and energy spent into it, Jean was sure Armin would insist on keeping the giant ass blanket fort they'd just built up for at least a week, but it was fun.
Moments later, Armin was crawling between the designated door sheets with his laptop and his spaceship carousel lamp. Jean lazily watched as Armin set the lamp up so they'd have light, and then shoved his laptop under the couch to 'keep it safe'.
"I thought we were gonna watch a movie?" Jean asked, twisting some to peer at Armin who was still half buried under the couch.
"We'll watch it later when I make the cocoa," came the muffled reply, and Jean shrugged, it was no skin off his back; before raising one of his eyebrows in confusion when Armin suddenly wiggled completely under the flipped couch.
"Now then," Armin said, as he crawled out from the other side, and Jean rolled over to look at Armin, before flushing when he noticed the telltale square wrapper held between pink lips. Armin raised his right arm triumphantly, a bottle of lube clenched in his fist, "Shall we christen the fort?"
'Fuck,' Jean thought, 'Armin's ideas are always the best.'