Author's Note: Ok, um, I don't know how I feel about this. Its not so much a dark Dasey as it is a twisted Dasey. It started with the part about Emily, and then the long fight they have.. And kinda spun out of control from there. In dark Daseys it tends to be Derek who is the bad one, and Casey is often a victim. I wanted them both to be bad. There are parts that are very much Cruel Intentions inspired, (I swear I'm going to try and stop making CI references in my Daseys… but its just too easy.)

Casey may seem OOC, but- I do find them both selfish, I love them, but they're selfish. I also think we have evidence that Casey can be manipulative(flirting with guys to sell Derek's product in The Poxfather, or milking her sprained ankle) It just seems like they would stoop to any level to one up each other, they've already used Lizzie and Edwin as pawns. his is kinda based on the idea of them loosing themselves in that battle.

This is the first fic I've ever rated M. Not for the sex, because I'm incapable of writing sex, but for the theme, and swearing I guess, but mostly, just because Derek and Casey are just really, really twisted. Again, just as a warning, this is NOT a happy story. Its screwed up and twisted. If you are looking for fluff or even normalacy, click back now.

I'm not even sure I like this story. Blah. It defiantly makes up for the fluff at the end of NHMLYD.

Disclaimer: Not mine. Still. Shame really.

"Derek? Are you ok baby? Can you hear me?" A voice from above him asked. He opened his eyes to see- Jeni, or Wendi, or Suzie? He didn't really know. She was just some girl he'd been talking to that night. Some girl he'd planned to bring home then never call. So why was she kneeling above him looking concerned? Why was on the ground? Groaning he lifted himself onto his elbows,

"What happened?" he asked. He tried to remember, but his head hurt too damn much to think, and there was a distracting dull ache in his midsection.

"That guy, just like attacked you. It was so scary. The police are here. You were knocked out." The blonde girl said. He groaned again, trying to make sense of what she'd just said and the images that were starting to surface in his mind.

"Casey." he muttered. He wasn't sure what had happened, but one thing had just become very clear, some how, this all connected to Casey. It figured, every time something hurt him and broke him out f his apathy, it was her.

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Then, much to his surprise, Emily leaned in and kissed him.

"Sorry," she said, breaking away and smiling sheepishly, "I've just wanted to do that for a really long time." She turned and quickly walked away. He shut the door behind her smiling thoughtfully,

"Don't be sorry," he said to himself, staring at the spot she'd just occupied, "I'm just sorry Casey didn't see it." he finished, smile widening at the thought.

Derek knew it wasn't normal, his preoccupation with aggravating Casey. He knew it wasn't just "sibling rivalry." He also knew it was wrong. It was one thing to hide her stuff and insult her, it was quite another to have enjoyed kissing her best friend, just because he knew how much it would annoy her. He was pretty sure it was a bad sign that second Emily had kissed him, he had pictured Casey catching them, and that had made him really, really enjoy the kiss. He told himself over and over again how messed up that was but it didn't change anything.

He experimented with it a little, to see if it was fluke, he'd flirt with Emily, teasing little comments but he found he couldn't even watch for her reaction, because all he could think of was Casey's. He didn't hear her little laughs or girly little comebacks, he just pictured Casey's enraged face in his head, and it made him really happy. It also scared him a little, so he backed off and dated Kendra.

Kendra was ok for a little while, pretty, blonde, fun and he had to admit, Casey's reactions to Kendra's clinginess made it much more bearable. It couldn't go on for long though, there was only so much being called, "Derry" a man can take. So he ended it with her and made Casey answer the door every time she came over to try and win him back.

So he dated more girls, random girls, blondes, brunettes, redheads, easy girls, stupid girls and it was fun, he got the satisfaction of Casey narrowing her eyes, or huffing in disgust. It wasn't enough though. He couldn't stop thinking about that kiss with Emily. So one day, spring of junior year he sought her out, flirted shamelessly with her, and charmed her back to his bedroom. He left the door a little open while they made out. Wrong as he knew it was, the knowledge that Casey would find out, made it the best make-out session Derek had experienced in a very long time. He rationalized it to himself, after all she'd dated Sam. Fair was fair right? She deserved this, and he was going to enjoy it.

He was hooked. Casey screamed at him, screamed at Emily, she stormed around the house and slammed doors. She tried to get his Dad and Nora involved, her insults towards him became nastier than ever. It was fantastic. So he made sure they were extra affectionate in her presence, he held Emily's hand in the hallways, and he always, always, left his door open, just a little.

Two months in Emily told him she loved him. He said it back, and she glowed. What he'd meant was, "I love what dating you does to Casey," but Emily didn't need to know that.

He knew Casey would keep fighting him about this, but he never thought she'd take the road she did. Around the same Emily confessed her love, Casey started showing up at all his hockey games, practices, and parties. He couldn't figure it out, she wasn't back with Sam, and she was ignoring him, so her presence puzzled him. He took advantage of the added opportunities to make-out with Emily with her watching, but he didn't put the pieces together for several weeks.

It wasn't until one day in the locker room when a teammate came up to him, smirking and said,

"Dude, your stepsister-" and then something Derek couldn't hear because all the blood had rushed to his ears. The smirk, the tone of voice, Derek knew them all too well. So he asked around- it seemed Casey had spent the last few weeks turning herself into a hockey groupie. There were hallway rumors she'd already hooked up with three guys on the team, not including Sam. It seemed the entire school had figured out what she was doing weeks before he did. Of course, they didn't know why she was doing it, only Derek knew that part.

So he struck back at her in the most fitting way he could think of. He had sex with Emily, and took delight in the fact that Emily, being Emily, wouldn't be able to stop herself from telling Casey. He stopped caring how wrong it was, his conscience stopped bothering him to "do the right thing." He stopped caring about everything really, everything except hurting Casey.

She responded by making a date with yet another hockey player, and making sure details of it got leaked around school. He had flowers sent to Emily in the middle of class he knew she shared with Casey. She accepted a senior hockey player's invite to the spring formal. He rented a hotel room for himself and Emily for after the spring formal, and made the sure the information was widely known. She went to a hotel room after spring formal too, with her date, whose reputation was worse than Derek's.

It seemed unending. At home their fights were fiercer, their insults cut deeper, and their family worried. By winter of their senior year, he was so consumed by their sick game, that every one of his actions, was calculated to some how get to her. Then one night, while he was watching her say goodnight to her date, a hockey player of course, and plotting out his next moved, he snapped.

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Derek was being lifted onto a gurney and into an ambulance. The police asked him questions and the blonde girl wept. He was annoyed. He'd been attacked, there were witnesses and even a tape, and they had the bastard in handcuffs, why should he have to answer questions? His head hurt too much for this, and his stomach was queasy. As for the blonde, her tears amused him. She'd known him for all of two hours. She probably thought they had a connection. He smirked at the thought.

"Mr. Venturi, do you know why this man would want to attack you?" The police asked for the tenth time as the EMTs took his vital signs and hooked him up to machines.

"How should I know?" Derek replied, "Look can we possibly talk about this when my head isn't throbbing?" he asked.

"We just need to make sure we have all the facts, and people are rarely attacked for no reason at all." The police said.

"Tell you what." Derek said, "Call Casey Macdonald and ask her why. I'm sure she has an explanation." He said. He closed his eyes, and smirked again. After all his attacker had said,

''This is for Casey," right before charging at Derek. He groaned again as a shot of pain moved through his stomach. He could hear the EMTs telling the police he had to get the hospital right away, and that they could ask him more questions later. Then drifted off to sleep.

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"This has got to stop." Derek said.

"What has to stop?" Casey questioned, sounding annoyed.

"This little game of ours. I'm sick of being messed with Casey." He said fiercely.

"I don't know what you're talking about, I was just trying to say goodbye to my date." She said her voice full of false innocence.

"Your date? Do you even know his name? Or is he just like, hockey player 38 to you?" Derek spat.

"Excuse me?" she asked, offended.

"You've become the Hockey team's go to groupie, and the saddest part is, you do it just to piss me off. Well guess what? It's working." He said.

"This from the man who made, Emily, my best friend, his personal whore. Hypocrite." She spat back.

"That's not a very nice thing to say about your friend, and for the record, Emily is my girlfriend. I treat her very well." he retorted.

"Oh please Derek. Don't pretend like you're the perfect boyfriend. Tell me, how many times have you cheated on her?" She said harshly.

"Never." he said, then smirked, "Don't need to, the girls a damn nympho, can't keep off me." he said.

"You're appalling." she said, "How can you stand there and say things like that just to infuriate me, but accuse me of dating the hockey team just bug you?" She demanded.

"Whatever Casey. You started this. You dated Sam." He said.

"That was different. I really liked Sam." She said.

"Oh you did not." He said.

"Yes I did. God Derek not everything I do is about you." She said.

"Yes it is, and no you didn't. Come on you two were the most boring couple in history and you know it." He said.

"What's your point?" she asked.

"That you started our little game." he said.

"You remember Vicky Derek? My cousin who I've spent my whole life hearing how much I look like? You went on and on about how hot she was, and then made out with her in our kitchen!" Casey spat.

"You had already shown obvious interest in Sam by then," Derek said.

"I had already listened to hours of Emily swooning over you!" Casey said, not even trying to defend her relationship with Sam anymore.

"That is not my fault and you know it. Face it, you started this." he said, "And you want to know why?"

"Please, enlighten me." she spat.

"Because you want me." he said, his voice low and dangerous, "because every time we fight you wish I would just snap and slam you against the nearest wall and fuck you senseless."

"Oh, but Derek, that would be wrong . We're family." she said with fake sugary sweetness in her voice.

"Do you think you could stop being a bitch for one second? Look me in the eyes and tell me I'm wrong Casey. Look me in the eyes and tell me this doesn't kill you." He said. She laughed.

"So when does the blonde girl come in to save you?" Casey asked.

"What?" he asked, totally thrown by her question.

"Well you seem to think we're living in our own version of Cruel Intentions, Emily is clearly Cecile, the innocent girl you're destroying. So now all you need is a blonde girl to save you from your evil, wicked ways, and we'll be all set." she said smirking.

"Must you be such a bitch all the time?" he asked.

"Actually, I'm usually very sweet. I only get this way around you." she said.

"I've noticed." he said dryly.

"And you want me in spite of it. How sweet." she said.

"Because of it actually." he said truthfully.

"How masochistic of you." She said.

"Are you planning on contributing anything to this conversation but snide remarks?" He asked.

"No." she said.

"I guess we're done then." He said, turning to walk out of the room.

"Wait." she called, clearly annoyed.

"Yes?" he said turning around.

"You're right." she said, defeated.

"I always am." he said, smirking and advancing on her.

"I loathe you." she said hatefully.

"Believe me, its mutual," he said, moving closer and closer to her, until she had to step back, and was against the wall. "But I figure we have two options." he said, placing and arm on either side of her, trapping her beneath him.

"I'm sure they're brilliant." she said her breathing heavy.

"Homicide or sex." he simply.

"Were you thinking we would kill each other?" she asked.

"I thought you, and the next guy that began a sentence with, 'Dude, your stepsister'." He said.

"I knew the locker room talk would drive you crazy." she said, smiling triumphantly.

"Shut up Casey." he growled, lowering his lips to hers.

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When Derek opened his eyes again, he saw he was in a hospital room, machines beeped all around him and a nurse was adjusting an IV bag above him.

"What's that for?" he asked.

"Good morning." she said, smiling, "Morphine for your pain. How are you feeling this morning?" she asked.

"Like death." he replied, "what happened to me?" he asked.

"Don't you remember?" she asked.

"Not the details." he said.

"You were stabbed. A man attacked you in a bar at about 1am. You had some severe bleeding and you hit your head pretty good against the ground when you fell. It might take awhile till you feel normal again." She said.

"Stabbed?" he asked. He hadn't remembered that. He knew they guy had attacked him, but he'd assumed he'd just been punched in the stomach several times. Damn, it wasn't even Casey's turn.

"Bitch." He muttered under his breath.

"What was that?" the nurse asked.

"Nothing," he said, "just, did they figure out why I was attacked yet?"

"I don't know for sure, but from what I've heard, it seems the man that attacked you is your ex-girlfriend's current boyfriend. I guess he was jealous or upset by something he found out or heard?" the nurse shrugged, "Like I said, I'm not positive. She's here by the way."

"Who?" he asked.

"The girl? Casey?" The nurse said, "Want me to send her in?"

'Please do." Derek said.

-------------------------------------------

"Arrogant asshole." she hissed.

"Stuck up bitch." he responded, glaring at his step-sister hatefully.

"Conceited bastard." she said, matching his glare with an identical one of her own.

"Whore." he spat.

"Prick." she said.

"I hate you." He said.

"Looking at you makes me ill." she replied. He kissed her fiercely.

"Run out of insults?" she questioned mockingly when they broke apart.

"No, I just couldn't take listening to your sad excuses for insults any longer." he said, hands gripping her arms tightly.

"Yes because, 'whore' is just so original." she said, reaching and hand out to grab his shirt and pull him down for a kiss. He threw her onto his bed,

"It may not be original, but its true." he said, before climbing on top of her and ripping off her clothes.

Insults were their foreplay. It was a ritual, a ritual that left them both bruised and tired, and yet, oddly satisfied. Angry kisses, fierce movements, slamming down, taking, getting, neither of them ever willing to give. A battle, even when the ecstasy made most movements involuntary. Never loving, always tinged with hatred, and yet they couldn't give it up. It kept them going for years.

They weren't faithful, although he'd stopped seeing Emily long ago, her sincerity had begun to bother him. They weren't kind or considerate to one another. They still did things just to get at each other. Things they knew would hurt the other one deeply. It was a sick game, and they both loved it. They were constantly trying to destroy one another. It didn't matter that it been years now since it began, or that other people often got caught in the middle. They didn't' care.

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"Don't you think this was going a bit far Case?" he asked as she walked into his hospital room and shut the door.

"He wasn't supposed to stab you. Moron." she muttered, walking over to his bed, "He was just supposed to start a fight with you, beat you up a little." she said, sitting in the chair next to his bed.

"See what happens when you send other people to do your dirty work?" he asked.

"Never again." she said, "why are you smiling? You were stabbed and you're grinning like a fool." she said.

"Because you came." he said, "You were worried about me." he mocked.

"I was not, I was feeling guilty." she said defensively.

"Nope, you care." he said, "God I love moments like this. I feel so triumphant."

"It's the morphine, its making you giddy." she said dryly.

"Whatever Casey." he said, still grinning, "I consider this a victory for me." he paused, "I do have a question though." he said.

"What?" she asked warily.

"It wasn't your turn. You can't do two in a row. That's not how this works." he said.

"No, it was most defiantly my turn." she said.

"How do you figure that?" he asked.

"Because, last week I thought-" she paused and took a deep breath, "I thought I was pregnant, and that made me want to kill you." She said.

"Since when would that automatically be my fault?" he asked.

"Since… recently." she said, not meeting his eyes.

"This day just keeps getting better." He said, smirking, "You're not though, right?" he asked.

"No, thank god." she said.

"So, just the fear made you want to kill me?" he asked.

"I told you, he wasn't supposed to stab you. Just smack you around a little." she said.

"What did you tell him Casey?" He asked, "And, if you've only been sleeping with me lately, who is he?"

"He follows me around a lot. He lives in my building, he's big and dumb. I told him you were my ex, and that I'd gotten pregnant and you'd abandoned me. So that was why I wasn't ready for anything new." she said, "I thought he'd just go fight you to defend my honor. I don't know he was crazy." she said.

"You interrupted my date you know." he said.

"More bar trash?" Casey asked.

"She cried as I was being put into the ambulance. It was very hard for her." He said.

"I'm sure reading is hard for her too." Casey said meanly, "She cried? Why?"

"I think she felt we had a connection." Derek said, laughing.

"How sweet. Too bad the only thing you're capable of loving is yourself." she said.

"Not true." he said.

"Oh right, and Marti, your one redeeming quality, the only time you're semi-human is around your eleven-year-old sister." Casey said, sounding less than impressed.

"Marti's a cool kid," he said, "but that's not what I meant. I mean this."

"This?" she said.

"Our sick little game, I love that. I love-" he said.

"Careful Derek," she said cutting him off, "I will hold you to anything you say here I don't care of you did just have a near-death experience and are high on pain killers."

"You." he finished, "and you love me. You've almost said as much tonight." he said.

"Maybe." she said.

"And we are going to spend the rest of our lives caught up in this fucked up little affair of ours. Because nothing we have with anyone else will, ever, ever come close. We'd be so bored with out each other, we'd go insane." He said.

"We're already insane." she said.

"Good point." he said, "But we're also pretty much stuck together."

"I know." she said.

"That doesn't make me hate you any less." he said.

"As always, the feelings mutual." she said, "you know, most people would find it impossible."

"What?" he asked.

"That we can love each other and yet still despise each other." she said.

"Well that's what makes us so damn special." he said, grinning.

"Or crazy." she said. He grinned again.

"Always so difficult Casey, if I wasn't an injured man-" he said, raising his eyebrows suggestively.

"Get better soon." she said, grinning, and leaning down to kiss him.

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And they lived twistedly-ever-after.

See this is why I say twisted, not so much dark. They do love each other.. Its just really, really screwed up.