Just a little something I wrote up real quick. As in the description, this contains yaoi and smut. If you don't like it, don't read it.
Armin waited in the mostly unused bathroom, tense and eager for Eren to get there. Since he'd joined the Survey Corps, it had been harder and harder to have any sort of alone time with Eren, since they both had training to do, and because of Levi's constant watch over Eren. But sometimes Eren could slip away for just a bit before going to bed, under the pretense of going to shower. Armin knew Levi would probably catch on eventually, but didn't think he'd mind much. If he vaguely knew where Eren was and what he was doing, he probably appreciated the short time he got to himself as much as Eren did.
Armin was standing in a corner of the showers, listening intently for footsteps outside. It was dark, but his eyes had adjusted a few minutes ago, allowing him to see the shadowy outline of the sinks across from the toilet stalls, and the doorway beyond that. Another minute ticked by, and Armin began to hear quick footsteps approach. His heart hammered in his chest, and he had a moment of panic imagining if the person coming in wasn't Eren. How would he explain to someone why he was just standing in the bathroom in the dark?
"Armin?" Armin squinted as Eren entered, holding a candle in front of him to navigate the dark halls quickly. Armin grinned, feeling his heart beat faster. He was here...
"Hey, Eren." Armin said quietly.
"Sorry it took so long." Eren approached, setting the candle on the floor right outside the showers. "I think Levi is starting to get suspicious..."
"How long do we have?" Armin asked anxiously.
"Just a few minutes...But if we take longer I'll just tell Levi I had to take a shit too." Armin nodded, already unbuttoning his vest. Eren snickered. "Eager?"
"I don't want you to get in trouble." Armin said, tossing his vest onto a bench. He went for his shirt next, unbuttoning it quickly and tossing it aside as well. Eren slipped his shirt off quickly, kicked off his shoes, and had his pants off in a flash. Armin's eyes roved his muscular body, taking in every inch of him in the dim light as he slipped off his own pants. They ditched their underwear next, then Eren turned the water on, making sure it was warm enough for them. Eren looked Armin over, grinning when he saw how hard he was already.
"Really eager, huh?" Eren chuckled.
"Oh, shut up..." Armin blushed as Eren got closer. Armin leaned his back against the cold stone wall and wrapped his arms around Eren, inhaling his scent with the steam. Eren kissed him briefly, just long enough to get himself going, then moved to Armin's shoulder, sucking and biting Armin's flesh. Armin bit back and moan of pleasure and grabbed Eren's hand, putting his calloused fingers into his mouth. They'd done this so many times now the dark or the time constraint didn't hinder them at all. They knew exactly what to do and when to do it. Armin sucked on Eren's fingers, getting them nice and wet with his saliva while Eren continued leaving a hickey on his shoulder.
Armin was still sucking on Eren's fingers when the brunette pushed him into the corner and lowered him to the floor. Armin leaned back and spread his legs apart as Eren took his fingers out of Armin's mouth.
"Ready?" Eren asked, moving his fingers toward Armin's entrance. Armin nodded, and Eren began kissing him again when he inserted two of his fingers, scissoring them a bit to prepare him. Armin gasped when Eren brushed his g-spot, and kissed Eren harder. His heart was still hammering in his chest, and he was so breathless he felt dizzy. Armin relaxed when Eren pulled his fingers out, then grimaced when Eren placed the tip of his member inside him. "Tell me if I'm hurting you." Eren said quickly, palming Armin's shaft for a few seconds to distract him from the discomfort. Armin moaned slightly as he adjusted (Eren was pretty big, and even after they'd done it as many times as they had it still hurt), then gasped as Eren fully thrust himself inside. Armin clutched Eren's shoulders, digging his nails in, panting heavily already.
"O-okay..." Armin panted. "Go." Eren began moving, thrusting quickly and hitting Armin's sweet spot with each thrust. Armin buried his face in Eren's shoulder, panting and moaning. His whole body felt alive with electricity, and with each soft grunt from Eren as he thrusted he felt closer to orgasm. His lower abdomen felt hot, and he felt like his insides were coiling tighter and tighter. He was digging his nails into Eren's back, and holding himself back from screaming with pain and pleasure. Eren thrust harder, hitting Armin's spot with everything he had. Armin felt his insides coil tighter, then with one more thrust they released all at once. Armin came hard, spattering Eren's chest. He threw his head back and moaned loudly, almost seeing stars. Eren clamped his hand over Armin's mouth, silencing the blonde so they wouldn't attract attention.
When his orgasm ended, Armin leaned against the tile limply, watching Eren with his eyes half closed. Eren kissed him gently and thrust a few more times, grunting as he came inside Armin. He pulled out, panting heavily, and stood up, getting under the shower to clean himself off. Armin forced himself to stand as well, feeling shaky and exhausted. He felt like he could curl up in a corner of the shower and just fall asleep.
But instead he turned on the shower next to Eren and began washing himself, feeling sweaty and sticky. Eren was already almost finished, showering at top speed so he could hurry to check in with Levi before going to his bed in the dungeons. Armin hated how Eren had to sleep down there, but it was the safest option for now, in case Eren transformed in his sleep.
Eren finished showering before Armin did, and shut off the water before hastily drying himself with a towel. Armin finished as Eren was putting on his shirt, and he wrapped himself in a towel to kiss Eren goodbye.
"Goodnight, Armin." Eren kissed him, careful not to get his clothes wet.
"Night..." Armin watched him leave, carrying the candle with him and leaving Armin alone in the dark bathroom. Armin waited for his eyes to adjust again, then dressed and headed back to the room he shared with Conny, Jean, Reiner, and Bertoldt.
The room had three bunk beds, and Armin slept on the top bunk of his, with Jean underneath. Reiner slept beneath Bertoldt, and Conny slept on the top bunk of the last one. They used the bottom bunk of Conny's for storage, and often hung towels and clothes off the sides. Everyone was inside when Armin came in, but only Bertoldt was asleep, in a weird position on his stomach with one leg dangling over the edge.
"Where've you been?" Jean asked, looking up from something he was drawing.
"Shower." Armin muttered, slipping off his shoes before climbing up to his bed.
"You spend a lot of time showering." Conny mused, tilting his head to look at Armin. Armin just shrugged and lay down, blushing and trying to hide it with his blanket. To his relief, no one questioned him any further, and in a few minutes Reiner had turned the lights out.
Armin turned onto his side, facing the wall, and pulled his blankets around him tighter, wishing Eren was there. It had been more than a month since they'd finished with the Trainees, but Armin was still used to sleeping beside Eren, since their beds had been next to each other for three years. He was still used to being kicked occasionally in his sleep, and listening to Eren's breathing and occasional whimpering when he had bad dreams. Now he just had Conny's snoring to listen to, and Bertoldt shifting around almost constantly in his sleep.
He closed his eyes, remembering Eren's scent and the feeling of Eren inside him, wishing he was beside him again.