No, it's too humiliating.

This was already getting weird enough. Billy knew he had to draw the line somewhere, because if not, there was no limit to how much he'd **** himself in order to get a little pleasure.

Anna was perched high on his ribs, straddling him. Her full weight wasn't on him, and Billy took the opportunity to do a quick sit-up, with the intention of twisting her off of him. As he did, he gripped her by her ribs and threw her to the side.

"Whoa!" she exclaimed as she tipped to the side. But she spread her knees out and was able to keep her balance and stay in the straddle. "I didn't expect you to have any fight left!" She looked over her shoulder at Billy. "You know...since I just knocked you out fair and square..."

He knew she'd never pass up an opportunity to rub that in his face, and she was proving it now. He tried to throw her off him again, but this time she was ready. Anna used her hips to slam Billy back into place on his back. Then she twisted, flinging her hand back in a backhand slap across Billy's face.

WHAP! It stung like crazy and rattled his brains, causing his head to jerk to the side. Billy went woozy, his tongue flopping out of his mouth as he tried to collect himself.

Anna moved up a little bit so she was sitting square on his chest. She lazily reached back and grabbed Billy's throat, partially cutting off his airway.

Between the slap and the light ****, Billy was feeling very lightheaded. He grabbed her wrist and yanked her hand off his throat. Anna had the leverage advantage, and responded by grabbing Billy's wrist and stuffing it under her calf, pinning it tightly between her leg and his body.

Then she returned her grip to his throat, and this time Billy didn't have a hand to fight back with. His little sister had him securely pinned, and one skinny arm was all that separated life and **** for Billy. His cock got even harder as he recognized her power over him.

She looked thoughtfully over her shoulder at him. "I probably could have been clearer." Billy wondered fearfully what she meant.

"If you'd voluntarily kissed my ass, you would have gotten a blow job..." Anna said. "But you're going to be kissing it either way."

And with that, Anna started inching backwards. Billy could feel her wet pussy sliding up his stomach and chest. He frantically bucked, trying to throw her off him yet again. But Anna had him pinned more securely than ever, and he was weak from the beating she had just delivered, his abs barely able to stay tense under her weight. Plus now she had her full weight pinning him, and although she was not heavy at all, it was still plenty to keep him down.

It was only a moment before Anna's beautiful butt took up Billy's whole view. He was powerless to stop her as she brought it down on his face, crushing his head into the carpet and completely stopping his breathing, blocking out all light and sound.

"Mmmmffff!" Billy moaned, the sound muffled by her butt. The feeling was amazing to Anna, who had never dominated anyone in this way before.

"Hahahahaha," she laughed happily. "How does that feel? Some part of you wanted this, remember!"

Billy's responses were getting more and more muted. His struggles were increasingly pathetic, and Anna was able to ride them out with no trouble. She wriggled her butt back and forth on his face, putting painful pressure on him and inhibiting his breathing even more. She held one of his hands in her lap, and his other hand was pinned by his side. The hand in her lap was groping at her thigh in a futile effort to dislodge her.

Anna kept laughing and rubbing her butt on Billy's defeated face. "I don't feel any kissing!!" she said in a singsong voice.

She paused, and could feel a very slight movement coming from Billy's face. Was it kissing? Or was her brother just trying to breathe?

It didn't matter, because soon enough, it stopped entirely. Billy's hand went limp, and rested harmlessly on Anna's thigh.

Anna's hands shot up to her cheeks, her face reddening with pleasure and embarrassment. "Ohmigod...did I just knock you out?" she exclaimed.

She twisted lithely around, straddling Billy's stomach and facing him. His head was tilted to the side, eyes closed, a string of drool running from his mouth.

Anna threw her hands in the air. "I knocked you out! First I knocked you out with my fists, then I knocked you out with my ass! HAHAHA!" She laughed at his knocked-out body.

Then she reached behind her and stroked his still-hard cock. His body barely responded...just a little groan and a shake of his head. Anna was disappointed in the lack of response, so she dug her knuckles into Billy's ribs.

"ooooohhhh," Billy groaned involuntarily, starting to come around.

"....Anna...what did you do....?" he asked her.

Anna crawled up and bent down close to his face, suddenly conscious of their compromised position. The house was big enough that Heather shouldn't have heard any of their fighting, but what if she came downstairs by chance?

"Shhh!" she whispered. When Billy opened his mouth to say something, looking blearily up at Anna's face, she slapped him lightly but sharply.

Billy's eyes rolled up in his head again, and he was out. "Darn it!" Anna cursed at herself. This time she hadn't meant to knock him out...it was almost too easy now.

She gave him a second to snooze as she put her sports bra and shorts back on. Once he started stirring, she went back and quickly straddled him again, grabbing his chin in her hand and pointing his face at hers.

"Not a word of any of this to anyone, right?" she asked.

Billy looked too scared to respond.

"I mean, if you want this to happen...which I assume you do," she said, reaching behind her once again to grab his cock for emphasis.

"I promise I won't tell!" Billy gasped out.

"Good...then I guess I will see you this time tomorrow night," Anna said. Billy nodded slightly.

"One more thing," Anna whispered, bending down so her lips were only a few inches from Billy's ear. "You're going to have to try harder...otherwise it'll be boring."

And with that, Anna smoothly got off him, leaving Billy on the floor with a historic case of blue balls and plenty to think about.