It was in the Cards

She didn't seem to object to that at all, instead she rubbed her butt against me, waking up my boner that had at long last decided to take a rest. It stirred against her warm soft flesh.

Pushing against her, as if it was blindly searching for a warm welcome.

Suddenly she stopped grinding.

"You have to move that thing. It's poking against my pussy, and that's way out of bounds, mister."

"Sorry, the little fella has a mind of his own, sometimes." I apologized, as I guided him away from the forbidden lands. Instead I made sure to place him firmly between her buttocks, with the tip pressing against her rectum. Figuring it would be sweet revenge to move from the one forbidden area, to an area that if not for our bet, would probably have been even more forbidden, even if I had not been her brother.

"There you go, all safe. We wouldn't want any accidents happening."

Just for emphasis I pushed my cock against her warm anus with every word. Just enough to tease her. If she would rather have my cock poking her anus, than having it brush harmlessly against her pussy, who was I to argue.

"Sure thing Kiddo. I do think perhaps you are just a little bit a pervert, enjoying getting his kink on with his sister. But who am I to judge? I'm the fool who bet her ass away."

As she spoke, she started grinding her ass, rubbing it against my cock, letting me slide against her crack. Pretty much sliding her anus along the length of my shaft. From the very tip, and to the root and back.

Every now and then she would change it up, when my tip was right against her star, she would clench and relax her buttocks, squeezing my most sensitive part.

I was finding it very hard to control myself. In this moment I was caring less and less that she was my sister. I wanted to bury myself balls deep inside of her.

But I managed some control.

Only grinding against her opening. There was no way I was getting inside anyway, dry as it was.

Instead I felt my climax getting close when she was about to switch back to just sliding my cock in her crack. As sexy as that was, right now I wanted her flesh clenching my cock, so I croaked out to her: "Don't stop, keep doing what you are doing!"

So she did. Pushing back against me as she relaxed her buttocks, then clenching tightly around the tip of my cock and pulling away, back and forth.

Suddenly, but not surprisingly, I came in a gushing torrent of cum.

The hours of what seemed like endless foreplay had put me on edge several times. Now all that saved up cum was being released right into her crack, sprayed right against her pulsating asshole.

As I came, I reflexively thrust forward slightly, as jet after jet was spraying out of me, and then it happened.

I met her thrust as she was going backwards, relaxing her butt, and I felt resistance, then the resistance yielded for a split second. I was inside of her. My sister. Maybe just an inch, if that.

Quick as it happened, she shot forward, startled.

Maybe she gasped or grunted something.

I am not entirely sure.

She pushed back against me almost without pause.

I don't know if it was the haze of horniness that I was in, or if I was still trying to make her quit the silly game. I don't even know if I believed in the game anymore. Or if I cared.

I only felt my need.

As she pushed back, I pushed against her, my cock still shooting a few lazy spurts of cum against her already cum soaked ass and rectum. We moved a little slower than before, and as I pushed myself firmly against her anus, it yielded slightly. I could feel the ring of her opening sliding around the very tip of my cock. Maybe just the last quarter inch. The last few drops of cum were delivered straight into her asshole. She ground her ass against me slowly, and I dared push in just a little further. Just another fraction of an inch.

suddenly the resistance yielded, and the entirety of my little head slipped inside of her.

It was the most amazing sensation. She was so unbelievably hot and tight. Her asshole was pulsating, fluttering around me, and if I had not already spent my load, I was sure I would have lost it at that very second.

Then the most marvellous thing happened.

Her ass tightened suddenly. Contracting so powerfully around my cock, that I was pushed out, along with most of the cum I had generously donated just seconds before.

Kaitlyn was bucking madly, out of control, as she moaned into the pillow, a powerful orgasm obviously roaring through her body.

Unable to help herself, or rather very intent on helping herself, depending on how you look at it, one hand was buried between her legs, frantically tending to her gushing pussy, as her other hand was gripping her breast tight enough to squeeze the juice from a coconut.

She kept on cumming for a full minute, and it was the most marvellous sexy sight I had ever seen. Almost enough to wake my little fella, but not quite. He was spent from having been hard for so many hours, and finally having had the most perfect orgasm, shooting cum directly into the asshole of my smoking hot sister.

Yeah, at that point, I didn't much care that she was my sister. She was a smoking hot woman, and I couldn't get enough of her.

Post nut clarity would have to wait until morning.

As she came down, she rolled over and looked at me.

"Well, I knew YOU were a pervert, but now it's starting to rub off on me too. Well. I guess I deserved a nice orgasm, with all the effort I've made to live up to our wager. But tomorrow I am going to win it back, you will see. For now though, I'm spent. So, if you need my ass for anything, just help yourself, or wake me up if you really must."

With that, she bid me good night, flopped onto her belly, and went to sleep.

I cuddled into her warm form, and put an arm around her.

"Only the ass, mister." She muttered into her pillow.

My pillow really, but she had claimed it at some point.

"Alright"

I moved my hand to her ass, letting my middle finger ride up and down her cum filled crack. Again, I couldn't quite resist the urge to punish her slightly, so I slowly let my middle finger play with her sticky rectum, rubbing it around the rim, then dipping it into her to the first knuckle. Taking it slowly, just playing around.

"That's nice." I heard her murmur into the pillow.

Not long after, I heard her snore.

I settled down, my hand remaining on her ass, finger resting in her crack.

As sleep also claimed me, my last waking thought was, "Tomorrow is going to be a great day!"