(Modern AU, Armin and Hanji are biological research partners working on a tough paper together)
Hanji was hunched over their desk. They'd been hunched over their desk for the better part of the day, typing away furiously. They were in the middle of a long investigation into a DNA mutation that had arisen recently, and did not wish to be disturbed. This, however, did not stop Armin, their research partner, from slipping into the room.
"Why is it so dark?" he asked, making Hanji jump. They swivelled to face him, annoyed. He threw open the curtains and slid open the window, ignoring Hanji's frown. "There, that's better." He turned to his research partner and grinned. "Guess what?"
Hanji gave a noncommittal grunt and swivelled back towards their desk, beginning to type again. Armin sighed. He made his way over to the desk and waved two slips of paper in front of his partner. This grabbed their attention, and they looked at Armin, curious. Armin just grinned.
"Come on, just tell me," Hanji said, rolling their eyes. Armin handed them one of the slips. Their eyes widened in surprise. "A coupon? For a spa?!" Armin nodded. "But I'm so close to finishing I can't-"
"No! You're coming with me," Armin cut Hanji off. "You and I have both been working hard, and yes, we are close to finishing this paper. But if you don't take a break, you're gonna burn yourself out. So, tomorrow, we're having a spa day, and we're gonna treat ourselves."
They met at the spa, Hanji wearing their work clothes, clearly intending to go right back to the lab after they were done. Armin shook his head in mock disappointment and led them inside. An impeccably dressed receptionist took their coupons with a smile, typed rapidly, and let them know the massages available. She also handed them a small bundle that included a towel, a cloth hairnet, eye covers, and suspiciously large white underpants. Throughout all of this, her smile never faltered, never twitched. This unsettled Hanji to no end, and they partially moved behind Armin to use him as cover.
"Was she creepy or what?" they whispered to their partner once they were past the reception. Armin gave a noncommittal shrug. Hanji rolled their eyes and followed him to the first room they went in that day. It was dimly lit, fairly humid, and the smell of incense hung heavily in the air. There were two massage tables right in the middle, a stone fountain to the right, a table covered in flowers, incense and pebbles to the right. In the far left and right corners, two room dividers stood parallel. Armin went left, Hanji went right, and they both changed into their spa-issued underwear. They took up their places at the massage tables, and two masseuses appeared. They got to work, Hanji's masseuse mumbling now and then how your back muscles are so tense, what have you been doing? Hanji relaxed gradually. At one point, while their masseuses were working on their sides, both their arms were outstretched, and their hands grazed. This set Hanji's heart fluttering, and they felt themselves blushing. Soon enough, however, the lighting, the smell, and the relaxing pressure from the masseuse overcame them and they dozed off.
Armin had to shake them awake, and he led them to the next station: a sweltering, stuffy sauna where they remained longer than either of them could actually stand. They left the sauna panting, red in the face, and gasping for air.
"Let's not do that ever again," Hanji gasped, and Armin nodded furiously. They took a few minutes to recover from the experience, and moved on to the last station. A white room, neither too warm nor too cool, with two massage tables covered in saran wrap. They both sighed inwardly in relief. Once they were in position, lying at their tables, two masseuses came in and proceeded to cover them in a brown substance. Hanji's first thought was that it was mud, but it was smoother and smelled far sweeter. Once they were fully covered, barely able to stifle their giggles, the two masseuses placed a slice of cucumber on their eyes and, for all the researchers knew, left them there to sit for a while.
At first, there was silence.
"Hey, Armin," Hanji spoke barely above a whisper. They snickered. "What do we do now?"
"I don't know," Armin hissed back, starting to laugh as well. "I bet you look hideous right now." Hanji let out a loud chuckle. "I bet you look like some sort of cucumber-eyed monster!" Armin's hisses turned into hysterical giggles.
"Shut up, you probably look the same," Hanji yelled. At this, they let their laughter loose, rising in pitch gradually. Eventually, one of their cucumbers slid off their face and fell to the floor with a wet splat. "Crap!"
"Look what you've done," Armin cried, nearly breathless with laughter. Hanji opened their freed eye and turned their face toward their partner. They saw him, lying still, all but vibrating from their laughter. A wave of warmth washed over their body while they looked at him. They'd never seen Armin so carefree, so relaxed. They'd never had this much fun just laying still. No, they'd never had fun with a day of relaxing. Their definition of fun usually revolved around work, and research.
They sighed a happy sigh and smiled. "Thank you, Armin. I owe you one."