Disclaimer: I do not own Thor, The Avengers, Avengers: Age of Ultron or anything to do with Marvel. I do not make any money from the writing of this story.
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Natasha Romanoff didn't immediately open her eyes when she came back to consciousness. It had been beaten into her from an early age to assess the situation she was in before opening her eyes, and remember how she got here.
Unfortunately neither were particularly pleasant, as her hands were securely tied behind her back and she was bent over some kind of device and strapped firmly down onto it, Natasha unable to pick the lock or slide her way out of the restraints despite her best efforts.
Surprisingly not even breaking bones help, as they instantly healed, which was a new one on her. Then again everything today was new for her. Not being defeated, that had happened before and if she got out of this it would happen again, but everything else was different.
She had certainly never fought an alien before. Not that it was much of a fight, the creature known as Sif beating her with ease and leaving her barely conscious so she could watch the other Avengers fall one by one to the supernaturally strong and incredibly smart fighter. At lease she wasn't the first to go down.
That was Ironman, as Tony was still furious over receiving those lewd pictures of Pepper Potts and he allowed it to consume him. Next was Hawkeye, followed by herself and then eventually Captain America and The Hulk. At least when she opened her eyes she saw the others weren't there sharing her fate, or worst bear witness to what was about to happen.
Acting Director of SHIELD Maria Hill had extensively debriefed her about what this Sif like to do to women, and there was little doubt in her mind that she would be next. Despite promises to the contrary Natasha couldn't deny there was part of her which was even intrigued, although she tried not to show it or any other emotion when the door she was facing finally opened.
That continued to be the case when instead of Sif a girl half her age scurried into the room with her head down, Natasha almost as disappointed as she was relieved. And she would have probably said something quippy, if there wasn't a large ball-gag stuffed in her mouth.
Slowly approaching Wanda bit her lip, and then revealed, "You know, I greatly envy you. The night my Mistress made me hers was the greatest night of my life. I have known greater pleasures since then, far beyond my wildest dreams, but nothing quite compares to the moment that what's left of your free will breaks completely and you become truly hers forever. Of course, such pleasure comes at a price. A price I have paid over, and over, and over again. Would you like to see?"
Natasha knew this wasn't really a question, that the girl known as Wanda, who was a powerful threat in her own right, was merely putting on a show for her boss. So she didn't react, and curiously awaited what Wanda would do next. What she couldn't have possibly expected was for Wanda to turn around and pull up her skirt to reveal she wasn't wearing any panties, and more importantly that her ass hole was gaping wide open.
The powerful Witch even reached back to spread her ass cheeks wide apart so the Natasha could see even deeper into Wanda's rectum, the super spy unable to hide her shocked at this display of submission made her. Or how intriguing she found it.
Wanda could still remember a time she wouldn't dare doing something so bold, but there wasn't anything she wouldn't do for Mistress Sif. Besides, Wanda delighted in acting like such a shameless slut and showing Natasha her future, that soon her butt hole would be gaping just as wide, if not wider given the mood her owner was in.
After defeating The Avengers Mistress Sif had announced she could think of no better way to celebrate than by wrecking her most powerful slave's ass, which was exactly what she did, Wanda eagerly pulling her short skirt up and out the way before bending over and spreading her cheeks for her Mistress.
Mistress Sif had slowly stretched her most forbidden hole, which had only just recovered from it's last butt fucking, and then pounded her back hole for a solid hour before allowing Wanda to teleport The Avengers back to their base. Well, all except one, and then psychically carry Natasha to the room they were now in and secure her in place.
Then Wanda was further rewarded with another ass fucking, this time Mistress Sif sitting in a chair right in front of Natasha while Wanda anally rode her so that the first thing the mighty Black Widow would see when she woke up was Wanda's butt hole stretching obscenely around Mistress Sif's cock as the shameless anal slave slowly bounced up and down.
Sadly Natasha hadn't woken up in time and Mistress Sif had left in search of another ass hole to abuse, most likely Darcy's. Indeed Mistress Sif had found her, eating Jane's pussy as usual, and now both assistant and scientist were face down and pleasing their Mistress with their most private holes. It was a show Wanda had been enjoying, until Natasha woke up, prompting her to psychically interrupt her owner.
Mistress Sif was now on her way, and it was up to Wanda to complete the second part of her oh so clear and detailed instructions for when Natasha woke. Instructions which Wanda delighted in completing, the broken slave continuing to taunt her soon-to-be fellow slave while exposing her ruined hole.
"Do you see Natasha? Do you see what's about to happen to you?" Wanda grinned as she looked back at the other woman, "You, oh mighty Black Widow, will be broken just like the rest of us and used for her pleasure. But don't worry though, you're going to love being her slave."
Just then Mistress Sif walked into the room, immediately making Wanda forget whatever else she was going to say. Especially as Mistress Sif didn't even spare the deadly Black Widow a single glance as she swiftly close the distance between them, pulled Wanda into her arms and shoved her tongue down her throat.