Except for "Keep it On," which I'd rate as "Mature" per AO3 guidelines, these are all sexually explicit.
asmallwave — "Caught"
Armin and Jean are "a thing." Eren doesn't know that, so when he and some other Survey Corps personnel find them in the woods, he thinks Jean's raping Armin. Needless to say, it doesn't go well for Jean after that. And, after they're marched into the mess hall during dinner and have to Explain Themselves To Captain Levi, it doesn't go well for any of them.
Jean and Armin are absolutely adorable in their clumsy awkwardness, Jean's solicitousness for Armin is sweet, and the smut, while not terribly explicit, is hot — well, until Eren rudely interrupts them, anyway. If embarrassment is your squick, you might want to pass on this one, but I found the ending funny. 3,416 words.
anonymous — "Fucking Eren"
Set early on in training. After fighting with Eren in the mess hall and thinking resentfully about how Eren doesn't deserve Mikasa's devotion, Jean goes off into the woods and tries to beat off to thoughts of Mikasa going down on him. But instead of imagining dark eyes, long black hair, and pale hands, he finds himself imagining green eyes, short brown hair, and tanned hands… 1,124 words.
anonymous — "The Perks of Being A Levi Flower"
Prompt: "Levi is a flower that Carla bought for Eren for his room and he watches Eren masturbate…. I have no excuse for this and I am not sorry." Neither am I. You get all that and
"plantacles" too. Grade-A crack that is also quite hot. And in character, insofar as photosynthesizing!Levi can be in character. 861 words. ETA:
There's a second fill there now called "Double Trouble,"
1,726 words, also quite hot and quite funny.
gaygaygaygaygay0 — "Keep it On"
Eren/Jean, with Jean POV. Things are getting hot and heavy between them until Jean starts to take his pants off — and Eren protests. The reason? Nudity reminds of him titans and is therefore a boner-killer. The dialogue is perfect: "Eren, if you haven't noticed, I, unlike Titans, HAVE A DICK. It's pressing RIGHT against your LEG, and it's telling me that you're being fucking stupid right now." "Well, tell your dick to shut the fuck up because we're not having sex naked."
Fortunately, Marco's there afterward to suggest a workaround to Jean. 909 words.
anonymous — "Dust Bunny"
Armin's on cleaning duty in an unused area of the barracks. He sees a clump of dust roll under a bed, chases it, and finds himself stuck there. And then
he learns that this part of the barracks, and especially this bed, aren't as "unused" as he thought. Featuring Reiner/Bertholdt, Eren/Levi, Eren/Erwin
/Levi (with the funniest line of dialogue you will ever see attributed to Erwin, I promise you), and, last but not least, Ymir/Christa. Poor Armin. Lucky us. 1,726 words.
anonymous — untitled
Armin sneaks into Eren's dungeon quarters after the trial and, after a joyful reunion hug, shamefacedly asks him to fuck him. Unsurprisingly for a couple of virginal teenagers, both of them are terrible at sex. Hilariously terrible. Sex in their case is a series of painful mishaps that culminates in them getting stuck together and yelling at one another. Which Levi overhears and decides to investigate. And then it gets even funnier (and more embarrassing for our boys). 3,265 words.
Variabile — "Get It Done"
On a rainy night toward the end of training, Jean and Eren are sharing a small field tent. Eren can't sleep because he has a boner. Asking Jean to go take a walk doesn't go over well. Jean, not knowing what the problem is, offers to help because Eren's his fellow trainee and you don't let your fellow trainee down (so to speak). And it's aawwwwkwaaaard.
The POV switches back and forth, they're both completely in character, and their dialogue and thoughts are screamingly funny: Jean really, really, doesn't want Eren to cry, because if Eren starts crying then there's a more than zero chance that Jean will start crying too (he's just built like that, alright, he's sensitive and his mum says that's okay so fuck you) and that, that would be the worst, like, the only way to save themselves from the embarrassment of that situation would be a suicide pact.
Oh, and there's some hotness, too. 5,729 words.
saekimchi — "Soggy Biscuit"
If you don't know what the title refers to, Wikipedia is your friend
(or maybe it isn't). Eren, Jean, Connie, Reiner, and Bertholdt are the ones playing the game. Trust me, the ending is not going to be quite what you think it is. I LOL'ed all the way through, beginning to end. 1,483 words.