Disclaimer: I do not own Supergirl or anything to do with DC. I do not make any money from the writing of this story.
Author's note: This story takes place during Season 1 of Supergirl, but there are no real spoilers.
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Alex Danvers tried to be a good sister. It was literally the story of her life. She had looked after her younger sister when they were little, been her best friend and even joined the DEO to try and protect her.
That was everything most people knew about her. Everything her Mom knew she did. Everything she was proud of. But there was something else, something she prayed no one would ever discover, that she had done in the name of being a good sister, and something she had tried so hard to stop doing.
But when she came home to find a completely naked Kara Danvers, a.k.a. Supergirl, kneeling in the middle of their living room and looking up at her so hopefully it was hard to remain strong.
"Kara, we've talked about this." Alex sighed.
"I know." Kara said softly, lowering her gaze, "But I... I had a really bad day."
"I know." Alex softly parroted.
It had been all over the news how Supergirl had failed to save a family of four when some lunatic blew up a bridge, most of the news reports not even bothering to imply that it was Supergirl's fault.
Instead they flat out said it, while mostly ignoring all the other families Kara had saved. Of course Alex, and everybody else, had tried to teach Kara that she couldn't save everybody, but Kara just wouldn't listen and always blamed herself for everything.
Alex could see it in Kara's eyes, something she had sadly guessed would be there as she reluctantly made her way home from the DEO base of operations in Central city. She just hoped she could avoid Kara's usual coping mechanism.
"But you should be eating ice cream and watching your favourite movies." Alex pointed out.
"You know that doesn't really work for me." Kara said softly, "And it's not just... the bridge thing, Ms Grant was super tough on me, and Winn just won't take a hint, and everything just seemed to go wrong today, and I just... I just can't take it anymore. So please Alex, help me."
Alex sighed and step closer, "You should just ask Ms Grant to be your Dom."
Kara blushed furiously, "I told you, she's straight."
Smirking as she closed the distance between them Alex quipped, "And I've never fucked my own sister."
There was a brief pause, then Kara looked up at her and boldly told Alex, "You think what we have is ugly. It's not. It's beautiful. And good. And... and it's the only thing that gets me through days like this."
There was another pause and then against her better judgement Alex kneeled down, cupped Kara's cheek and softly said, "Nothing about you could ever be ugly."
Kara smiled, closed her eyes and leaned into the touch, while Alex desperately wished she could believe her own words. Well, Kara had always been beautiful, but the love they had for each other wasn't pure and innocent.
It had been perverted by Alex's selfishness. After all, for all of her power and strength Alex had no doubt that Kara would have taken no for an answer that first-time.
That she wouldn't have physically force the issue if Alex just had the strength to say no. But she had never been able to resist the sight of Kara on her knees, so instead Alex lent down even further and kissed her little sister for what had to be the millionth time.
Countless times Alex had promised herself this would never happen again, had told Kara it would never happen again, but it was a promise she just couldn't keep, and as their lips connected again Alex almost forgot why this was so wrong. Almost.
But this wasn't one of those heated kisses were Alex forgot everything including her name, a.k.a. the type of kiss she was hoping to someday have with someone other than her sister. It was a slow, gentle kiss, the type of which Kara allowed her to have complete control, and the type which she knew enhanced Kara's feeling of submission.
Kara always had let Alex be in control because she was terrified of hurting her. Also it was therapeutic to submit to someone physically weaker than herself. And it felt natural. Everything with Alex had always felt natural to Kara, and she would never understand why humans had so many hangups about sex.
To be fair she had been too young to know whether such things were so forbidden on Krypton, but she liked to think not. She liked to think it was a place they could have been happy together, at least when she allowed herself such bittersweet thoughts.
But even on this planet there was an arguable grey area, given that Kara was Alex's adopted sister instead of a blood relation, although Kara didn't like to say it out loud as their sisterly bond was just as important to her as their sexual relationship.
Suddenly Alex broke the kiss, got up and smiled, "Don't go anywhere."
With that Alex walked into her bedroom, a.k.a. the one they shared pretty much on a nightly basis, even if a lot of the time they were just snuggling under the bed sheets and watching trashy TV, which Kara always enjoyed, just not as much as this.
Like the well-trained sub she was Kara remained on her knees patiently for several long minutes, confident that her big sister would return to begin her favourite sisterly act.
Sure enough after some rustling around Kara heard footsteps approach and found herself smiling up at her sibling, who smiled back before producing a little box from behind her back. Before Kara had time to wonder what was inside it Alex opened the box and the superhero cried out softly in pain and betrayal.
"Kryptonite?" Kara questioned, looking up at her sister with big blue eyes.
"Enough to neutralize your powers, but not do any permanent damage." Alex said sternly, taking the little black collar with the tiny green stone attached to it out of the box and then further explaining, "I took it from a pair of handcuffs which were able to restrain your cousin. If it's too much for you I can get something smaller, but I thought you'd appreciate the experience of truly losing control. And maybe I'm hoping it will finally put you off wanting to be my slutty little lesbian sub. Although I'm not holding my breath."
"Please don't." Kara said softly, before quickly clarifying, "Please don't hold your breath. Nothing could ever stop me from wanting to be yours."
"We'll see." Alex mumbled, before pushing, "Now, do you want to try the collar?"
