Firefly, Kaylee/Simon(/River), staring at the ceiling and watching her watching them
Simon's on top of you, and you thought it would never happen. Much less that it would happen with both of you on the floor by a pile of cargo where just anyone might walk by and see you. But what can you say? You two had been alone and things were just shiny and you finally got up the nerve to kiss him and it seems like maybe he'd been waiting for that for a long time because he didn't have the nerve to do it himself. So now you're here, clothed only enough to be comfortable against the metal floor, and Simon's lips are on your neck and his hand is between your legs, and things couldn't be better.
Except she's looking at you. River is standing on the walkway above you, staring with an expression that might be fascination or disgust or something else entirely. It seems like you understand her better than most, but you've never been good at reading her face and knowing what she's thinking. You gasp when you see her, and Simon seems to assume it's in pleasure. You think it's better that way. If he knew she was watching, he would stop, and that's not what you want at all. Not when things are finally going the way you want.
You ignore her, and look at the ceiling instead. And then you decide it works better to close your eyes, though you can't help checking sometimes to see if she's still watching. But you try not to get distracted, and pretty soon you're so enthralled with the feeling of Simon on you and in you that you can't be distracted (but you notice she's still there), and you and Simon come at the same time, seeming satisfied and breathing hard. He rolls off you and the smile on his face is so shiny it makes you giggle.
And then you remember her. You're afraid he'll see her and know she was there and it'll ruin the whole thing, but when you look back up she's already gone. You must look confused, because Simon asks you if there's something wrong. You tell him no, everything is shiny, and let's do that again sometime, but maybe somewhere a little more comfortable and a little more private.