We put the agreement Maddie and I had reached into effect immediately—after all, spring break had officially begun when school'd gotten out that day. Mom was due home in a few minutes, though, so we didn't have time, then, to accomplish much more than get our clothes back where Mom would probably think they belonged. And we couldn't think of a believable reason why we should study that evening, so we didn't have any opportunity to make out, either.
Saturday afternoon, Mom and Dad made their usual grocery-shopping run. The garage door had barely quit rising when we met at the base of the stairs. "Your room or mine," I asked her after the ensuing kiss had ended.
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I didn't get to sleep in on Monday, the first weekday of spring break. No, much as I liked sleeping in on mornings when there was no school, this was even better.
I woke to find Maddie naked in bed beside me, playing with my morning wood where it projected through the fly of my pajama pants.
Of course, I had to ask: "Mom and Dad! Are they gone?"
"Do you think I'm an idiot? Too?" she asked—and punctuated her question with a moan as one of my hands found a tit and tweaked her nipple. Naturally, we'd have liked to go somewhere for the break, but Dad said we couldn't afford a trip, both because we didn't have enough money in the bank and because he and Mom would have had to take leaves without pay while we were gone. And the plans we had for the week, the plans Maddie and I had formed on Friday, were much more interesting.
Then she added, "They left for work a few minutes ago. We've got the whole day together alone."
I shrugged out of my pajama tops and we rolled toward each other, to meet in the middle of the bed. Her naked body felt marvelous against me, and I reached for the drawstring of my bottoms as we shared another kiss. When the kiss ended, I said, "I'm going to fuck you, now."
"No," she said. "I'm going to fuck you!" and she pushed me onto my back. She reached for the waistband of the pajama buttons and pulled them downward. Seeing what she intended, I raised my ass off the bed, and the pants were quickly down around my knees. Saying, "That's good enough for what I've got in mind," she threw a leg over me and rose to her own knees to straddle me.
Then we both watched my cock slide into her pussy as she lowered herself onto it. Not long after that, we exploded in each other's arms and I pumped surge after surge of my cum into my sister.
===||<>||===
It was Wednesday, late in the afternoon, and Madison and I lay together in her bed, recovering from our second fuck of the day. She had rolled her naked body against mine, and each of us had an exploratory hand roaming gently over the other's body.
I turned my head to look at her. "Do you really think this will work?" I asked. We had fucked twice, now, on every weekday so far this week—once each morning when we woke up and once each afternoon, shortly before we expected Mom home from work. We still had Thursday and Friday to go, and we expected to fuck at least twice on each of those days. And once on Saturday, as always. And, somehow, we had also managed to work on our math together after supper every night. Of course, that, too, had led to our usual make-out sessions, during which each of us had eaten the other.
She raised her head from where it had rested on my shoulder and grinned at me; then she kissed my neck not far from where her head had been. "I'm not sure I care," she said. "I'm glad we agreed to try this. I don't think we would have made it even this far—let alone the whole week. We'd be fucking each other several times a day by now. Do you think it's going to work?"
"Well… no," I admitted. "We wouldn't have made it. But I don't think I'm getting tired of fucking you."
"I'm not getting tired of fucking you, either," she said. "But we sure would have gotten tired of trying not to."
"You got that right," I said. "I was getting tired of that last week."
She snuggled in a little more tightly against me. "Me, too," she said.
"This is much better," I pointed out.
"Yeah," she replied. "We don't have to feel guilty about doing something we'd agreed not to do."
"That was a good idea you had. But what if…" I started, and then quit without finishing.
"What if it doesn't work?" she finished for me. "Not to worry. We won't be any worse off than we were before break. We might as well enjoy the break, since we can't go anywhere."
"I sure enjoyed that!" I remarked.
"Me, too!" she crooned as she snuggled in tightly against me.
We lay there for a while, each enjoying the feel of the other's body and the other's hand roaming our own. Finally, she asked, "What time is it?"
I looked over at the clock. "It's about half past four," I said. "We'd better get up and get ready for Mom to get home."
===||<>||===
We continued through the week, fucking every morning after Mom and Dad had left for work and every afternoon, right before they came home. We did miss our Friday afternoon fuck, because Andrea—who had also stayed home for the break—wanted Maddie to come over that afternoon. When I objected, Maddie said, "Andrea knows I'm free. Needing to come home and fuck my brother instead wouldn't be a satisfactory excuse. At least, not one I can use." I couldn't argue with that.
We also missed our evening make-out session on Friday, because Dad took us out for dinner that evening to "celebrate spring break." We thought it was a pretty corny gesture, but we did enjoy a good restaurant meal. Even though we didn't get our usual evening "meals" because of it.
So, in spite of our activities earlier in the week, we were especially horny on Saturday afternoon when Mom and Dad made their weekly grocery-shopping trip. So horny, in fact, that we didn't make it to either of our bedrooms. We wound up fucking halfway up the stairs. Maddie said we weren't going to do that again; she didn't like the way the hard risers dug into her back. I tried out the position she'd been in, and I had to sympathize with her. And I admitted that it hadn't been so good for my shins, either—though it sure had been good for my cock.
After we'd gotten dressed following that Saturday afternoon delight, we sat together on the couch, Maddie's now-fully-clothed body resting against me, my arm around her, to await our parents' return with the coming week's food supplies. "Are you sick of fucking your brother yet?" I asked her.
She stroked my thigh, where her hand rested on it. "Not at all," she said. "It just gets better and better. Are you sick of fucking your sister?"
"Well," I dissembled, "I don't think I could get it up for you now."