For the prompt: "Eremin: Eren finds out Armin reads m/m erotica."
Eren can understand why people underestimate Armin.
He's short (but not as short as Levi, who doesn't have this problem) and a little bit on the feminine side, but what most people get hung up on is that Armin looks like the picture perfect image of every Renaissance cherub or angel ever.
Eren himself falls prey to this every now and then, perhaps glowering too hard at other people on the bus that linger a little bit too long on his boyfriend, or being surprised every time Armin initiates something a little bit more daring than he would normally suspect.
Eren can't figure out why he can't just realize that Armin is not the picture perfect innocent he looks like he could be, especially when he has long memories of nights spent in one of their bedrooms, ears straining for parents coming home, rutting urgently and listening to Armin talk, and fuck, but Armin can talk, and it's absolutely filthy and -
Point is, Armin is not innocent. Not at all.
And considering what they've done themselves, Eren shouldn't be surprised when he borrows Armin's computer to look up his math homework and finds it open to some of the most detailed, explicitly written gay sex he's ever read in his life.
Eren splutters incoherently and whacks his knees on the computer table when his brain finally recognizes what it is. This, of course, grabs Armin's attention from where he's reading their English homework on the bed.
"Eren? Are you -" he stops talking as he sees Eren's face, which is bright red. "Oh damn, did I leave something up? I have got to stop that, one day Mom is going to find out and I'm going to be dead - Eren? Are you all right?"
Eren finally snaps back to himself.
"Yeah, yeah, fine, just - just a little surprised." Armin stares, looking a little bit confused, before laughing.
"Eren," he says, still laughing as he stands up from his seat on the bed to slide into Eren's lap. Eren places his hands on Armin's waist, more on instinct than anything else. "Eren. I've had your dick in my mouth. And you're blushing because you found gay smut on my computer. You - really?"
Eren looks down at his hands before mumbling a quick "yeah".
Armin is still laughing when he pulls Eren's face up so he can kiss it.