Disclaimer: I don't own "The Vampire Diaries" or any of it's characters, so I'm not making money with this story.
It's been twenty years by now. Caroline never regretted her choice to be with Klaus, despite his obvious flaws, but she had to learn that he hides things in the shadows that she doesn't want to see but never fails to notice. She learned to love his family, his twisted, tainted family, but there's something odd about Klaus and Rebekah. Sometimes when Caroline watches them she feels like a voyeur – there's just something about their intense stares and their desperate whispers that makes her shiver. She never speaks to Klaus about it, of course – he may love her, but Caroline knows better than to arouse his anger.
Her subconsciousness notices it before she does. It's the little things that make her frown - the way Klaus is always a thousand times more hurt when betrayal comes from his sister instead of his brothers. The awkward moment when Caroline wants to buy Rebekah a beautiful bra as a christmas present and Klaus knows exactly what size she is wearing. It irritates her how he grants Rebekah the first dance at his birthday party, swirling her around and making her laugh like a child. Caroline tells herself that she is insane. She shouldn't even wonder about the way Klaus looks at Rebekah's new designer jeans, because honestly, no one knows fashion like he does, but no matter how hard she tries she can't shake the feeling that he's staring at his sister's legs instead.
The siblings may be irritating when living in harmony, but they are far more scary when they fight. Caroline saw twenty years pass, along with a string of Rebekah's lovers – and, you can trust her on that, it was no small amount – and she watches Klaus chase off or kill most of them. Of course she understands – he wants to be a good big brother, wants to shield his little sister from the evil of the world, but at some point it doesn't only become ridiculous, it becomes gross. Not all of the boys are golden ones – some are liars, some are thieves, some are something far worse. But there's also alright guys, nice guys even, like Alex, a doctor with an excellent reputation and a great humor and everything that Rebekah is looking for in a man. He even willingly accepts her offer to turn him into a vampire – Klaus kills him the morning after.
Events like that happen several times. It always goes the same way: Klaus kills, Rebekah shouts and cries, but barely a week later they act as like nothing ever happened. It's just odd, the passion that Rebekah gives to her lovers and the indifference she shows when it comes to their death. It's like she never excepted something different anyway. Caroline tries to defend her interests one day, but neither Klaus nor Rebekah want to listen. It's like she intervenes with a topic whose complexity she simply can't understand and the original sister never liked her anyway, no matter how hard Caroline tried.
The most shocking secret is revealed to her by Klaus during a relaxed dinner. They eat in a cute little French restaurant, have a couple glasses of wine and Caroline dreamily listens to Klaus telling stories about the past. It comes out of the blue, during a conversation about traditions, that he says: "Me and Rebekah were about to be married when we were human. Of course the event never occurred after my father cursed me as a vicious bastard. More wine?" He drops the information casually, like it is nothing, and Caroline can't do anything else than nod, but it chills her to the bone.
Once Caroline walks in on them, fighting passionately. They are too caught up in themselves to notice her, standing on the balcony, watching them. Klaus shouts at her, something about her cruel plans to leave him for a human nobody. Sometimes it's like it's the only real fear on his mind, keeping him awake at night – the thought of his precious sister leaving him behind. Rebekah screams back, claiming her freedom, her rights as a woman and her right for love. She insults her brother, threatens to leave him for real if he keeps behaving like this. Right in this moment Klaus pulls the dagger out of his jacket.
"You won't go anywhere, sweetheart!", he explodes and raises the weapon furiously at her. "I will have you dead before I lose you!"
Rebekah screams and tries to hit him to get a hold of the dagger, but his hybrid powers overpower her. In a flash he has her pressed up against the wall, the front of the dagger pointing right at her heart. Rebekah starts to cry uncontrollably. "Why are you behaving like this, Nik?", she whimpers. "This is not the deal we were making! I promised to stay with you, despite your cruel lies and your dreadful killings, but all you do is threaten me and denying me the freedom you promised me!" Pure desperation marks her face as she wraps her arms around his neck, trying to soften his stone cold eyes. "Let me go!", she whispers with tears in her eyes.
It takes him an endless second to answer. "I'm sorry, Bekah", he says and strokes her blonde hair in a grotesque, gentle way, "but you are mine." He smiles at her, but it's not sweet, just creepy. Rebekah stares at him with wide eyes as he leans in to her. In sudden fear Caroline closes her eyes, afraid of what she might see. In a flash she is gone, trying to forget everything and leaving the decision about Rebekah's life and death in the hands of her beloved brother.