A/N: The sin is lust, and the prompt is "a friend comes to visit".
"Good evening, Lily," James smiles.
Lily does not bother to move from her desk, where she is busily drafting a Potions essay.
"How did you get in here, Potter?" she asks.
She sounds irritated, but James knows her too well to take her seriously.
"I have my ways," he tells her. "Nice place you've got here. The Head Girl gets lots of room and such a lovely bed. I'm sure that will come in handy later."
Lily sends him an exasperated look, and James simply gives her a suggestive wink in return.
"If you're not going to tell me how you got in here, you could at least tell me why you're here," she sighs.
"Can't a friend casually drop in for a visit?" James asks. "I'm wounded that you would be so harsh, Lily."
He moves closer to her, his grin widening with every step.
"James," Lily laughs. "You are completely ridiculous."
"Does that mean you don't want to kiss me right now?" James smirks.
Lily crosses her legs and smiles innocently at him.
"I hate you," she informs him. "I really do hate you, Potter. I hope you know that."
James leans down so that he is looking directly into her eyes, and Lily nearly shivers from the feeling of his warm breath on her lips.
"I didn't ask you how you felt about me, Evans," he whispers. "What I asked is if you want to kiss me right now."
His hand is on her thigh now, his thumb slowly tracing circles on her skin, and Lily finally gives up.
"Bloody hell," she mutters.
And then she kisses him.