My Sister's Bet

Edited by: Sam. Thanks!

*****

"Get up from that lazy butt of yours!" screamed my sister from downstairs. I had been alone in the house, playing LoL in my room for hours. When I heard the front door open, I knew Peach had come home. Peach wasn't her real name, obviously, but one given to her by a boyfriend long ago. Soon the name stuck with her friends, and even our older sister Aria used it from time to time. I dared to only once, and stopped when faced with her withering stare. Our parents even used it once in a while, but never understood why we laughed and Peach squirmed. You see, Peach had her nickname because her perfect ass looked like the rounded curves of a firm peach. I always called her Peach in my mind.

Anyway, that's besides the point. I had no idea why Peach would ask me to get off my butt, but I would soon find out. Peach burst into my room without knocking, and I thanked my luck that she hadn't come earlier. In fact, a quick glance under my desk revealed that one of the tissues I had used was still on the floor, probably glued there. In any case, she didn't notice it. "Get up big brother!" she said, a strange expression on her face. I turned around briefly, but kept my focus on the nearly done game. Peach was back from her daily run, and was dressed accordingly: black spandex from ankles to neck. As usual, I could detect a sports bra, but no panties. Damned little tease. She repeated "I said get up!"

"What's your problem?" I asked, irritated.

"Forget about that game, I have a favour to ask you!"

"Asking me a favour by shouting at me, calling me lazy and interrupting my game? Some nerve!" I replied, knowing the game was... and there it was. Another victory.

"You done now?"

"Yes, I am." I turned around fully, resisting the temptation to look at her body. She was damned fine. Both my sisters were, even though they were incredibly different. Peach took after mom; lithe, tall with an all natural, all genetic athletic build. Aria, instead, took after dad, but it worked. It worked damned well. She was smaller than Peach, but with a lot more curves: hips, thighs and breasts that would put most women to shame. I shook my head and tried to focus on Peach. "What do you want?"

"I want you to get in shape!" she said, with that strange expression on her face again. She seemed somewhat angry, determined and tried to cover it with a smile.

"What? What the..."

"I mean it! It's almost midsummer and by September, you have to be in great shape!" she said, adding a winning smile after that.

I paused, looked at her for a bit, unable to figure what she had in mind. "What the fuck is going on?"

To my surprise, Peach took a deep breath and sighed as she let herself fall backwards on my bed. She groaned before explaining herself. "I took a bet. With Jennifer. Oh... that was such a bad idea!"

"A bet? About me?" I asked, dumbfounded. Jennifer was Peach's best friend, another very hot girl with a passion for training. They were both instructors at our local gym. She barely knew I existed, ignoring Peach's gamer brother as if I didn't exist. This bet didn't feel good. At all. "What did you do? What did you bet?"

"Shit!" another sigh. "I bet Jen that I was such a good trainer that could get even you into great shape in four months. Three and a half to be more precise."

"What the fuck would you do that for?" I asked.

"I don't know... I thought I could... But now, seeing you sprawled on your chair in front of your game..."

"You're crazy! Even ignoring your talents as a trainer, why do you think I'd even accept?"

And then my sister giggled. Looking at her as she lay on my bed, I could see her breasts, a large B cup at best, jiggle on her chest. "Well, I told Jen that if I succeeded, she'd have to go out with you on a date."

"The fuck? You think I wanna go on a date with her?" I replied, stunned.

"Hahaha... Yeah right. I know you may not like her or the way she treats you, but I see you looking at her. You'd really say no to a date with her?"

"Well... I do have a decent amount of principles and integrity..." I replied, weakly.

Peach lifted her head from the bed and looked up, genuinely puzzled. "Really?"

"Yeah... I do. But, maybe, not that much!"

Peach laughed, before getting up. "So you'll do it?"

"No way!" Her face fell. It was almost comical.

"What do you mean?"

"I mean that I'd like a date with her, but not if it forces me to starve myself, not play video games, abuse my body and work out hours everyday. She's hot, but there's more to life than a single date with a hot girl, a date that wouldn't amount to anything else afterwards in any case."

"Hmmm. Shit."

Peach jumped back on my bed, on her stomach this time. As she was thinking about my answer, I glanced at that perfect ass of hers. Pretty much identical to Jennifer, in fact. I'd eat that ass. Either of them in fact, sister or not. Damn! I even felt a tingle in my cock, looking at her now. But suddenly it hit me and I asked her : "Er, what happens if you lose?"

Another groan, as she buried her face in my pillow. "I have to record a video of me telling the entire world that she's the greatest trainer in the world, much better than I will ever be, and post it on Facebook. Crap!"

"Nothing worse?" I said, smiling, staring at her ass while she couldn't see me.

"That's utterly bad!" was her quick reply as she turned to look at me. And then, a quick "And stop staring at my ass, pervert!" But her tone was light.

In fact it was an old joke, and I replied with my usual. "If you don't want me staring, don't wear those pants."

I was expecting her to shake her head, but her eyes got bigger as an idea bloomed in her head. "Think about it brother! A date with Jen, with an ass nearly as nice as mine! Think about it, imagine it, picture it in your mind!" She was grinning again.

I couldn't exactly tell her that I didn't need to see Jen's ass given that hers was right there. "Nah... Sorry sis, it's too much work for a meaningless date. Besides, you know I won't get to do more than look."

"Fuck!" she buried her face in the pillow once more. But suddenly she lifted it again and said "What if she—" then stopped, before adding "Staring at my ass again?" Peach laughed. "Come on big brother... you know there are websites with nice asses all over the web." She laughed and tsk'ed me, but not with malice. Peach had always been sweet with me, which has not been the case for Aria. Once she had caught me staring at her generous cleavage and had screamed her outrage. I think Peach took my stolen glances as compliments, which, in fact, they were. That was part of it, at least.

Still on my bed, with her ass still on display despite her comments, Peach's expression changed. I could see it on her face: she'd had an idea. I didn't know if I should be worried. "What I'm about to tell you needs to remain absolutely private. Understood?"

I thought she wanted to spill something about Jen, but in fact it turned out quite different. "Ok sis, I can keep a secret."

"You like to stare at my ass?"

"What? Are you high?"

"Just answer the question, lazy brother!" she was now grinning, and looked like a wolf ready to pounce.

"Er... Sure, of course... You knew that!"

"Yes. So here's the deal. If you agree to train with me for the next three and a half month, I'll let you stare at my ass as long as you want. I'll even wear sexier clothes while we train."

"What? Are you serious? You'd really do that... you'd do that instead of recording that video? Wow, that's quite an ego, sis!" I laughed, but it was to cover my nervousness.

"You bet! So, interested? Think this ass," and she gave it a slap, making its firm flesh bounce, "can motivate you into great shape?"

"You are positively crazy, Peach!" I dared use the name, given the circumstance.

She opened her mouth in surprise, then grinned. "Oh you want that peach right here?" she asked, slapping her ass again. "You want that? Well get off your own ass and put on some gym shorts and a tee-shirt. We're going running."

She then left my room without waiting for an answer. Stunned that it had happened so fast. I cried out "Now?"

"Of course! Let me change and we'll hit the street!" she replied from her own room.

Five minutes later, we were outside in the driveway and Peach simply began running. She had spent the last hour running, but that wouldn't stop her. I followed her, still utterly stunned by what was going on. Then again, I immediately enjoyed my reward. Peach was wearing the same black camisole top with a sports bra, but now had a pair of very short spandex shorts, no panties. Fuck she looked good! I could feel the beginning of an erection as I followed her, and wondered if this wasn't going to cause problems. I was only 19 years old (Peach was 18), and fully aware that erections could happen regardless of the situation.

Soon enough, I fell into a sort of trance as I ran. I was nearly hypnotized by the sight of her cheeks bouncing up and down, twisting sideways slightly with each step. She was essentially naked. I had never seen her run with those shorts before, and they looked like black body paint. They even ran up very tightly in her crack instead of stretching taut between her buttocks. She was essentially naked except for the colour. Despite my arousal, my erection didn't grow fully, and it was just barely uncomfortable.

What soon became uncomfortable was my exhaustion. I really was in bad shape. I said a quick "Peach!" as I stopped, bent over, trying to regain my breath. She came back and stopped really close to me. She turned her back to me, saying, innocently "I'll give you two minutes, then we run back home." I could see her legs very close to me, and eventually realized that I was seeing the back of her thighs. When I turned my head, I found her ass right next to my face. Fuck it looked good! Despite my exhaustion, my cock responded, twitching in my tight shorts. I was maybe 6 inches away, actually too close to see it properly, but I didn't complain. The sin of her thighs was covered with a fine sheet of sweat, making them glow in the sunlight. "Fuck..." I breathed. "Fuck... damn that's a nice ass!" Peach laughed, then slapped my own ass before starting to run again. Shaking my head, I ran after her and tried to find that trance-like state liker earlier.

When we came back home, I went inside to change into my swimsuit and quickly dove in the pool. Peach and I were still alone, and as I relaxed in the pool, I head her voice from the upstairs bathroom window. "Are you sure about this? You really wanna try?"

"Well, why not... I do want to get in shape, and this is probably the best way to get there..."

Two minutes later she walked out of the house with her tiny red bikini. I stopped swimming and came to the edge of the deck, looking up at her. "Peach, you're absolutely gorgeous... I don't know if this type of compliments is part of our deal, but I don't care." I knew I was red-faced and very nervous, but I thought it would be well received. It was.

"Ah... Thanks brother. And, you know, that special permission to stare at my ass can be extended even when we're not training, but only when we're alone..."

With that she placed a towel on the deck, right next to the pool, and lay on her stomach. I spent the next fifteen minutes staring at her entire body as if my life depended on it. When she turned on her side with her ass facing me, which was probably very uncomfortable, I got an extra five minutes to look at her ass with her curves accentuated. "My turn for a question now... Are you sure you don't mind your big brother ogling you like a pervert?"

Peach turned around, on her other side to look at me. "To tell you the truth, I never minded. Sure it's strange, but what's the harm in looking?" As I was grinning, she continued "You know we're not done for today, right? That was just a twenty minute run, in other words a warm-up. In five minutes you're coming out and we'll start working on your abs."

"Aw..." I groaned.

And so five minutes later I was on my back on the grass, trying to get to twenty-five sit-ups. It was relatively fun, though, as Peach was squatting at my feet, holding them down, pushing her smallish breasts in a very advantageous position. They looked bigger, and seemed to grow each time I came back up. After that it was push-ups, with Peach kneeling right in front of me. Every time I was up, I could look at her long, firm thighs. From up close, very close. Then we went through a series of stretching exercises, with me trying to mirror her movements. Slightly out of breath, I said "Looking at you, I'm beginning to understand why you're so popular at the gym..."

"Pfff... Silly boy! I don't go there wearing my bikini for all the perverts!" she replied, winking at me with a smile. "Stretch! Go lower!"

About an hour later she finally said we were done. I knew she had seen my semi-erect cock through my swimsuit a few times, but she didn't seem to mind. She joined me in the pool for a few laps as I simply lay there exhausted. Contrary to my relationship with Aria, Peach and I had always been friendly. Sure she teased my about my gaming and I sometimes let her know what I thought about some of her boyfriends. On the other hand, we never really hung together. Nevertheless, those twenty or so minutes in the pool after training were surprisingly pleasant. Maybe it was because I could be honest with my glances or compliments, but we really connected. When she climbed out, glistening with dripping water and sexy as hell in the sun, she turned and looked at me "Now, remember: your entire body will be really tense tomorrow morning. Don't worry, it's normal. But know this: we will train anyway. If you're nice, I may even massage you before so as to ward off the worse of the pain."

"Don't worry about me, I'll be up for it." I replied, slightly afraid of being sore.

"Yeah... Hopefully not too, ahem... up, for it." was Peach's reply, with another wink.

"Shut up!" I replied, laughing. The little minx was talking about my cock.

She was laughing as well as she went back inside the house. I did my best to stretch in the pool, trying to prevent most of the soreness. In vain. When I woke up the next morning, everything hurt. From my ankles to my neck. I laughed, remembering that I had thought that about my sister's spandex. I groaned when I tried to sit up in bed. It hurt, it hurt bad. I suddenly heard Aria's voice form the corridor "He's up!" followed by Peach's muffled voice from downstairs. Aria came in my room, without knocking.

"Doesn't anybody knock in this house?"

Aria ignored my comment. She was already dressed for work: she spent most of her days at music camp, teaching young kids the rudiments of her art. Despite that type of work, and the clothes that went with it, I could still see the shape of her very large breasts and hips underneath. She said "Peach says that you have to get up now." And then she disappeared. Less than a minute later I heard her leaving the house. I then heard Peach running up the stairs (running!) to stop in my door frame.

"Ready, big brother?" She was leaning against the frame, making her left hip stand out sharply. Peach had nowhere near the generous and feminine hips of her older sister, but in this pose, with her tiny red bikini again, the effect was remarkable.

"Ready to stare at your glorious beauty in the morning light?" I was still sleepy, my head foggy.

"Oh... Thank you sweet brother. I meant ready for your massage?"

"Er, OK." I saw that she had a small vial of oil in her hand. "You're really going to massage me?"

"Sure! Didn't I say so?"

"Wearing that bikini?" I asked, knowing that my boxers would fail miserably at hiding my erection.

"Why not? Want me to go and change?" Peach asked, playfully.

"No! I mean no, no... It's alright."

"I thought so... pervert. getting turned on by his sister... sheesh! That's so bad!" she was laughing, and so was I.

"Well... don't be surprised when you ask me to turn around, OK?"

"What? Really?" she asked.

"Oh come on... You little tease!"

Peach laughed as I turned on my stomach. She climbed on my bed, straddled my thighs with her own and I felt her skin touch mine. When she began working her magic, I was in heaven. I was moaning and groaning, enjoying everything she was doing, from the nape of my neck to the sole of my feet. Softly, she said "There you go big brother... time to turn around." And so I did, keeping my eyes closed. I knew I was rock hard, and that it would be very, very obvious. Peach didn't say a word, but worked all over my chest, thighs and calves anyway. After a few minutes I opened my eyes and caught her looking at my cock. "Who's the pervert now?" I whispered. She recoiled in surprise, and I saw fear briefly appearing on her face. Then she grinned and laughed. "Guilty as charged! Sorry big brother... That wasn't part of the deal."

"Bah... If you're going to wake me every morning with a massage in that bikini, you can do anything you want with me."

"Good! That's good, big brother..." she said, accentuating the word big. We both laughed, dispelling the tension. "In that case, I'm going to ask you to run another twenty minutes again!"

"Aw crap..."

"Get up, change and drink a tall glass of orange juice. Then we'll run!"

Insanely, this became my routine for the next few weeks. When we'd be alone in the house, Peach would wake me up with a bikini-clad massage, we'd run for twenty or twenty five minutes, swim around a bit, she'd then let me see her ass as she sunbathed, cleavage as I did sit-ups, thighs as I did push ups and the most imaginable angles as we stretched and worked out in the back yard. It never became boring. Her naughty plan was working wonderfully well. Even after just three weeks I generally felt better, even if I was sore all the time. And Peach was happy. And we were growing a lot closer. It's as if the special physical intimacy opened the door to other types of intimacy. In these weeks, we've learned a lot more about each other. Even about usually private things. It was a very warm feeling, discovering my sister like this.

After 8 weeks, only 5 left until the arrival of Fall, Peach began worrying. I wasn't going to make it. Jen and her had set specific goals, and while my initial progress had been very good, things had slowed down. Despite all the stimulation, I was getting really tired of working hard and eating a strict diet. And, while I wouldn't say it, staring at her great ass and body every day for hours had lost some of its interest. Not much, grant you, but still... Peach knew we had to change something.

And the solution presented itself because of a special date with her boyfriend. She had talked to me about it for weeks, and when she came out of her room all dressed up for a fancy evening, I was shocked. It's strange how context can affect perception. I've spent the last 2 months with Peach nearly naked for hours everyday. That red bikini didn't hide much. But tonight, seeing her in her new dress all cleaned up, that was quite a shock. Later, I realized that it was her cleavage. Bikinis were nice and all, but I was learning that a nice push-up bra could do miracles. I spent the entire night thinking about her cleavage. I hadn't been a big fan of her make-up, or the way she had arranged her hair: an all natural look fit her a lot more, in my opinion. Yet that push up bra... Fuck! That night, and not for the first time, I masturbated myself to sleep thinking about my sister.

The following morning, there was no massage in bed. Peach had returned from her evening very, very late. I woke up first, broke my fast with the rest of the family and Peach was still sleeping when everybody left. I crashed in front of the TV, glad of a break this morning. Around 11, I heard Peach waking up, going to the bathroom and heading back to her room. I grinned and went up, carrying her bottle of oil. When I cracked the door to her room, I whispered her name. I smiled as I heard her croak a gravelly "Yeah?"