Sam is working, he's always working, immersed in his laptop and piles of books, researching this, verifying that, compiling information on a million different topics. This is usually where Sam is when he comes to visit, and he does come, he comes often, uninvited and unannounced, and always when Dean isn't around. Sam will be reading his screen, his hand on the mouse, in the middle of scrolling down a page, and he'll hear it, that flutter of wings, a heavy sound, like thick leather tarps flapping in the wind. "Cas?" Sam says quietly, but really he knows it isn't Cas, because he doesn't know how but he can tell, somehow, he can just tell, when he hears that sound, who it is that's standing behind him. And he stops what he's doing and becomes very still, not daring look behind him, because what if it's Cas, or what is it's not? He swallows quietly and closes his eyes, telling himself, turn around, but he doesn't want to see, so he just sits there. And finally, when he decided to take the chance, he readies himself to stand up and turn around, he never gets the change, because a mouth hovers by his ear and whispers, "Hello, Sam," and it sends a shiver through him that reaches his very core and he has to stop himself from trembling.
"Lucifer," Sam responds, careful not to let his voice betray him, his feelings, the fear, and other things, too, things he can't name, and doesn't want to.
At first Lucifer doesn't say anything, doesn't do anything, but then he whispers Sam's name and Sam feels a rough hand slowly moving along his cheek, caressing it gently, and Sam's breath catches in his throat. Lucifer's hand moves to Sam's chin, then his neck, and slowly, so slowly, down into his shirt, and the devil's hand is rubbing Sam's chest, and Sam is petrified, frozen, even though this has happened a thousand times before, it never gets easier, because every time is like the first time.
Lucifer's lips softly touch Sam's cheek as his hand continues to rub Sam's chest, and then his other hand snakes down and he pushes it under the bottom of Sam's shirt, and his fingers run along Sam's ribs, stomach, and naval, and very carefully begin to work their way downward—
Sam can't suppress a shudder then, just one, that violently racks his body for a split second, and Lucifer feels it and wraps his arms around him more tightly and says soothingly in his ear, "Shhh, Sammy, it's all right," and Sam leans back into his embrace, because he wants to feel safe in someone's arms, even Lucifer's.
Lucifer feels this and gently withdraws his hands from Sam's shirt and instead wraps them around Sam's shoulders and begins gently rocking him back and forth, pressing his face into Sam's neck, whispering "I love you, Sammy," over and over, and Sam pretends he doesn't hear this, because the very idea of being loved by the devil is so foreign, and so terrifying, he doesn't even want to contemplate it.
Even more terrifying is the concept that, through all his fear, Sam might actually want the devil to like him, and, on some level, might actually like him back. Lucifer's presence was overpowering, petrifying; when he was in the room, the aura of power and evil was awe-inspiring, and filled Sam with dread, and yet, just a tiny bit, there was comfort, too, and safety, but not enough that Sam would ever act on it, because Lucifer was the devil, the devil, and it was lies and trickery and evil, because how could it be anything else?
Lucifer's embrace loosened, and he swiveled Sam's chair around so they were facing each other, eye to eye, and they remained that way for a moment before Lucifer leaned in and pressed his lips to Sam's, passionately, lovingly, clutching the sides of Sam's head, and Sam leaned into the kiss just slightly, not quite returning it, and goosebumps rose on Sam's arms and neck, until finally Lucifer broke off, panting slightly. He looked earnestly into Sam's face, and Sam thought he could see longing in the devil's eyes, but said nothing, only watched in apprehension, until Lucifer seemed to give up, and said, with a sigh, "Bye, Sam," and there was a distinct trace of sadness in his voice. Then a flash and that heavy flapping sound, and Sam was alone, feeling immense relief, and, perhaps, a twinge of regret.