Derek is starting to feel that his stepsister really really doesn't quite "get it".

"Casey!" He says exasperated, as she bounds up the stairs after him, following him into his room.

"I need space!" He says it slowly, in the same tone of voice he used when he tried to explain "The Big Bang Theory," to Marti. Of course, that ended even better than this-mostly because he decided to just show Marti the song by the Barenaked Ladies and be done with it.

Unfortunately for his sake, no record store he knows stocks the CD "Leave Derek alone and Let him have his space, you crazy woman named Casey." Apparently, Casey doesn't know the song very well either-because she sets herself down on his bed, staring up at him patiently.

"Well Derek?" She says sweetly, and Derek curses the god he doesn't believe in. Casey-this is so unfair-she's milking it for all it's worth and it isn't fair. And yes, Derek will act like a five year old if he wants to, thank you very much.

"Casey," Derek says, deciding that a new tactic might work better than his pitiful pleas. He smirks, his classic smartarse smirk, the one he wears right before he gets angry, and says "Out. Now."

Nothing happens.

Casey stays sitting on his bed, her legs swinging, biting her lip, staring at him. And-and dammit, why would she do that, when She knows it drives him crazy?

Derek glares at her for a few seconds before deciding to switch his game plan, once again. Instead, he falls forward, straight on top of Casey, hopefully crushing her once and for all.

"Do you dream about this, Derek?" Casey says. She has that pompous tone in her voice and Derek rolls of her, angrily.

"Get away from me," He says, and now he just sounds plain pissed off.

Casey sighs and rolls close to him.

"Derek, it's cute."

Derek makes no response, intently gazing at the wall in front him. His crush on Casey is anything but cute. It's disgusting-it's awful-it's terrible-it's predictable.

"I'm glad you told me. I was really starting to get worked up about your behaviour towards me. Now, I know it's just cause you're in love with me!"

Who does Casey think she is? Barging in here, all triumphant just because she found out Derek's secret. She has no right to toy with his emotions like that. None, whatsoever.

"You're so arrogant," He mutters, resentment building up in his stomach. "Besides, it's your fault that I like you."

"I'm arrogant?" Casey scoffs. "Yes. Says the King of Cockiness. Derek, I can't believe you would try to blame your crush on me on me. That is just so typically you, always willing to blame someone else for your actions, try and get out of your responsibilities."

"Well, if you didn't act like a crazy psychotic bitch, maybe I wouldn't have this weird attraction for you." Derek replies, completely missing the point.

"Derek. I'm a teenage girl with a chest and a great body. That's why you like me. Because 'I'm hot.' Or, maybe, because you can't have me. I'm off limits. Dangerous. It's not me you like. It's what rules you would be breaking to have me."

Derek shakes his head, desperate to make her understand that it wasn't about being rebellious, or her hot body (which of course, was always a plus). It was about their fights that left them breathless, panting hard and almost kissing, the sexual tension between them in everything that they did. The way Derek felt about Sam and Casey-how his stomach had twisted into anxious knots and he prayed to God that Sam wouldn't take anything away from Casey.

It was in the way Derek liked Max, because Max was a respectful guy and wasn't about to push Casey into anything she didn't want to do.

It was the way Derek had pushed Ralph towards her, because he knew she'd never go for it and he found that all too amazing to watch.

But it wasn't about him being dangerous or rebellious or irresponsible. It was about him wanting to hold her and kiss her and talk to her, like a normal girlfriend so badly that it made him nauseous.

The way he had always secretly hoped that Casey would grab his shirt after one of their arguments or wrestling matches, and press her lips against his, and whisper "I love you," on his mouth.

"Case you just don't get it, do you?" Derek sighs, frustrated. "I want you. Everything about you. All your baggage and shit and your insane womanly behaviour. Every part of it, I want."

Casey stares at him intently for a few seconds and then says,

"You're laying it on pretty thick now, aren't you Der-Bear?"

Derek slams his head against the bed headboard as he wonders about how many ways he can kill Casey while making it look like self defense.

"Derek. You do not like me. Get it through your head. You don't like me, you never have, you never will. You and me fight. We're brother and sister, it's what we do."

"Step-brother and sister, Case. Step-don't-don't ever forget that."

Casey sighs. "Okay Derek, give it up. Stop going so Lifetime on me. I mean, this is rich, even for you."

Derek punches his pillow in frustration.

"Do you still not believe me?" He snaps, breathing hard.

"Yeah, Derek, because, like you have a crush on me."

"What, is there another reason you've been stalking me twenty four seven?"

"I heard you on the phone with Sam the other night. And I know you left your door open so I would hear. So instead of freaking out about it, like you wanted me to, I planned to drive you crazy by doing all that I did this week. And it worked."

Fuck Casey. That was so unfair. She'd spent the entire week leading him on, brushing her hand on his thigh, leaning down so his eyes could travel to her cleavage, snuggling up to him while he watched hockey on television and following him around like a lost puppy.

"You mean, you knew? Before Dad told you? Before I told you? You knew that I liked you?" Derek asks, and his voice kind of cracks because-yeah, it kind of hurts. She was fucking around with him and he let himself believe that she returned his feelings.

He had never intended to leave his bedroom door open that night-he mustn't of clicked it shut properly. It was closed enough to fool Derek that it was shut, but, he supposed, if he was talking on his bed his voice would be audible to a person outside the hallway. It did seem kind of planned-Casey, walking down the hallway, right passed his room, just as Derek uttered out "I like Casey," to Sam. It was something he would do, but-he wouldn't.

"Derek?" Casey questions gently, but Derek doesn't bother responding.

He is so mad with her right now, so very angry, so he stares at the cieling, hard, blinking back the tears threatening to fall.

Casey gently places her hand on top of Derek's and he snatches it away quickly.

"I don't want your pity," He says, his voice even. Even if he lost, he is determined to win.

"Derek-you can' can't be serious...can you?" Casey asks, her voice faltering.

Derek breathes through his nose, hard. "Does it matter, Princess?" He spits bitterly. "I think we all know what kind of person you are."

"Derek, you can't blame this on me!" Casey exclaims incredulously. "How was I supposed to know you weren't lying? This is exactly the type of thing I would expect from you! For all I know, you could still be lying now! Are you?" She adds, as an after thought.

Derek closes his eyes and heaves a great sigh. What he wouldn't give to go back to the days of Edwin, Marti and his Father. Before Nora, before Lizzie, before stupid Casey.

He doesn't understand why Casey is affecting him this much anyway. She's just his stupid step sister. He shouldn't be getting so worked up to the point where he wants to cry about it.

"Derek, you know know that, I love you, even if we fight. But...I love you, as a brother. You get that, right? We're just brother and sister. To me, there is no 'step'. You're my brother. I'll always look out for you and I know you'd do the same for me."

So, apparently Casey finds it completely okay to flirt with her brother? Does this mean she approves of incest, too?

"So this entire week was a prank?" Derek whispers with a heavy heart.

"Derek-I'm so sorry. I didn't know you were serious. I thought you just said it to drive me crazy, to make me want you. And then to laugh when you reject me. So I thought I would win by doing that to you first. I just wanted to beat you so badly, Derek. But..regardless..I..I can't say that I return the feelings Derek. But I feel terrible for toying with your emotions like that. I'm so sorry, I'll do whatever it takes to make it up to you."

With his hands covering his eyes, Derek quickly wipes away all the tears and uses all of his strength to summon up one powerful laugh.

"Casey, Casey, Casey," He laughs, shaking his head. "When ever will you learn, my dear Step-sis? The jokes on you. I can't believe I got you, again. Will you ever stop falling for my sentimental facade?" Derek planted a fake smile on his face. "Ah, the art of winning."

Casey stared Derek down for a good ten seconds before standing up and aiming a pillow at his head.


A/N: Hey there! Firstly, I want to point out that I am a MAJOR Dasey shipper and I believe in it with every little bit of my soul. But I also thought unrequited love between Derek and Casey would be an interesting concept to explore. I chose Derek to have feelings because he rarely shows his vulnerable side and I must admit, it is a side that I enjoy seeing. It also allows more creative control for the author because Casey's anxious side is so defined and Derek's is really well hidden, really giving that levvy for imagination. When I first started to write this, I honestly thought Derek and Casey would end up making out on his bed by the end of the story. However, the more insight I wrote into Derek's mind the more I realized that the denial of Casey is what made the show. I think it would be awesome if they got together in LWD, but I also feel like it would be Jumping the shark, per say. The chase between these two is the most fun to watch. Anyway, I just wanted to thank you for being amazing and reading it :) btw i love constructive critisims and would be prepared to take any on board :) Thank you!