All the characters in this story engaged in sexual acts are over 18.
*****
I'm Sam, my twin sister is Rosie. We have both always been about two kilos overweight. In my case it was belly, for Rosie it was bum. She's medium height and build in every respect except for that rounded tush. She has shoulder-length hair which has always been blonde, her rounded face is soft, eyes sparkling blue; she's genuinely pretty, but I have to confess I've always been attracted to her body. Her breasts are not large, nor small, but they are pert and firm.
We were close growing up, then she married at twenty, divorced at twenty-four. I had a long-term relationship from age eighteen to just before our twenty-fifth birthday. Rosie took me out dancing and drinking for our celebration.
At first it was a real fun night. We'd only just got reacquainted in the last few months and still had lots to catch up on. She's a really sexy dancer, which might explain why she attracted so many appreciative stares from blokes (and a few from girls, too).
At one point she had her arms around my neck while she gyrated to the beat. She wore a simple tight black dress. I remember thinking, somewhat sadly, that there was not one girl in this place to compare with my former long-time girlfriend Annie except one - and she was my bloody sister.
Much later, in my apartment, we were buzzed and getting cozy. I lay on the couch, she sat lengthways on it with her head on a cushion against the arm, so her back was in my lap. At one point, the conversation went like this:
"No, you've missed my point Rosie. I'm saying the main reason some people don't have sex with just anybody is guilt. For example, most couples wouldn't cheat on each other even if they couldn't be found out, and it's because of guilt. Some single people wouldn't sleep with a married person because of morality - that is, they'd feel guilty."
"Maybe. Are you saying that, say, family members would have sex with each other if they just put the guilt aside?"
"I hadn't thought of that, but I guess so. Yeah, why not? Without guilt, maybe they would."
We sipped our drinks. It had started as one of those drunk-intellectual debates but had just taken a weird turn. I don't know what Rosie was thinking but I had suddenly thought about having sex with my own sister, at first in the abstract way, then thinking about 'what if'.
I continued the theme: "OK, so. What if a brother and sister were mad hot for each other, and they waved a magic wand and guilt no longer existed. What would stop them?"
"Jesus Sam! A brother and sister?"
"Yeah. Hypothetically."
"Any brother and sister or you and me?" She smiled up at me, meeting my eyes. Hers sparkled with her own daring, but I think I blushed a little. "Oh. Um, well... OK! OK yeah - if you were horny for me and I was desperate for you, without guilt, wouldn't we?"
"Oh nice one bro. I only have to be horny but you'd have to be desperate!"
We laughed and it lightened the heaviness in the air. "No, that's not what I meant. Hell no bloke would turn you down if you gave him half a chance!"
She pushed her tease further: "Oh really! OK, so. What if I gave
you
half a chance? In your argument, you'd have a go if only it wouldn't make you feel guilty?"
"If only it wouldn't make us
both
feel guilty. Yes, sure."
She giggled a little, which made her tits jiggle. Suddenly I felt the beginnings of arousal. In my dulled brain I realised that, in a roundabout way, I'd just admitted out loud to my own sister that I would fuck her if only guilt didn't get in the way. I noticed that Rosie was deep in thought, idly stroking my knee with one hand. She sipped her drink again, then almost sputtered it out.
"Wait! You just said... Oh shit. Did you just say, well, you'd
do it
with me?"
"If there was no guilt sure. You're super-hot so why not?"
"I don't know how to answer that."
My cock answered for us. I was looking at her tightly-covered breasts right there in my lap. Clear, creamy skin against that svelte one-piece black number. Cleavage. One black bra strap visible. I imagined those delightful orbs naked. I imagined
her
naked. Despite what I'd drank, my cock stirred. It poked the middle of her back. I hoped she didn't notice and at first she pretended she didn't. We stayed like that in silence for some minutes but my cock ached, hard as ever, the knob hard against her.
I gulped before asking: "What are you thinking?"
She sat upright, I thought to get away. Instead she reached behind herself inside the tight black dress to awkwardly unsnap her bra then lay back down. She looked up at me and said: "OK. This is a test. I'm willing to suspend my guilt if you can. If you feel guilty, you won't touch my tits. If I feel guilty, I'll stop you if you try."
Perhaps she thought this was still a debate, or maybe she thought I wouldn't. But in three seconds, I'd put my glass down and reached inside her bra cups. My hand found her nipple straight away and I pinched it. She twitched but didn't stop me, so I pushed her dress out of the way and went for the other. I stroked my sister's breasts tenderly, timidly even, expecting her to push me away at any moment.
I was looking into her eyes. Her naughty-girl smile vanished, she bit her lip and closed her eyes. In that instant our game went from a debate to a seduction. Now I began
stimulating
her, not just touching her. My sister's tits, about which I'd fantasised many times, were now in my hands and she was clearly loving my caresses. Her breathing deepened and she pressed her hard nipples into the palms of my hands.
I brought her to earth briefly: "So what do you say?"
She opened her eyes, giggled and said: "I don't know whether we passed the test or failed it."
"Want me to stop?"
"You want to stop?"
"No."
"Then don't."
I misinterpreted. When I took my left hand from her breast onto her bare thigh then slid it up under her dress, briefly touching her damp panties, she flinched and jumped off me.
"Oh wait. No. I didn't mean..."
"Sorry sis. I just...thought.."