Ben and Susan’s unusual relation – part 3

“What are you up to back there?” she asked.

“Just trying something,” I said.

I went back a couple times to make sure I had plenty of Susan’s girl-cum for lubrication, I didn’t know how easy this was going to be. Even when I thought I had enough her butt still seemed really tight and I had difficulty even just getting my fingertip past the entrance.

“You gotta relax a little,” I told her. “I have no idea how you thought sex was going to work.”

“You should know by now I can be a little impulsive,” she said, making a good point. “And it’s hard to relax when I’m excited. Maybe you should just fuck me first and try it after when I’m all calmed down.”

“I won’t feel like bothering with it afterward if we do that,” I said. “Although….”

Susan might have something there, if I got her concentrating on sex she wouldn’t be focused on her ass so much. It was worth a shot.

She moaned appreciatively as I guided my cock into her pussy and immediately angled her body to make penetration easier. Even before I was fully inside she was rocking back against me in time with my thrusts, quickly establishing a rhythm with me. I’d long ago been tired of jokes about how we should be able to read each other’s minds since we were twins, but when we were having sex sometimes it felt like we actually could on a subconscious level. We just moved so naturally together despite being relatively new to this particular phase of our relationship.

I kept my finger pressed against Susan’s tight butt, waiting for it to loosen a bit and eventually it did. Slowly, almost reluctantly, her muscles relaxed enough to let just the tip of my finger inside before clamping down again when she realized what had happened.

“It’s in, isn’t it,” she said.

“Yes it is,” I confirmed.

“Feels a little weird, not too bad though. Doesn’t hurt.”

Susan’s movements had become hesitant as she processed the new sensations, then slowly returned to normal as she got comfortable with the idea. Before long I was able to push my finger farther into her butt and started gently finger-fucking it.

“Mmm, okay that’s feeling kinda good now,” she said. “Kinda sexy too.”

“You think you’d like doing it for real?”

“Yeah, I definitely want to try it. I’ll have to work on that.”

She was losing any self-control she might have started with and rocked back against me with increasing force. I had no idea anal-play would be so much of a turn-on for her and she probably hadn’t realized it either beforehand. There was no doubt in my mind that it would be more than my finger in her butt in the near future.

Only moments later her pace reached its most frantic level and her pussy squeezed my cock hard. I loved the feeling of my sister cumming, and as was not uncommon my orgasm followed close behind hers. I could rarely resist the sensations she produced when she came while I was inside her.

Susan gradually slowed as her orgasm finished and the last of my semen emptied into her. She rolled onto her side as I finally pulled out and smiled at me a little tiredly. I lay down facing her and we watched each other in silence for a minute or two.

“So we’re really going to resort to blackmail are we?” I said eventually.

“It’s not blackmail,” Susan protested, though her heart wasn’t in it enough to make a convincing denial. “We’d just be trading favors. I didn’t tell Miss Reid, she lets us borrow her class. Quick and easy.”

Under different circumstances I probably would have taken advantage of Susan leaving herself wide open with her last comment. She’d get that it was a joke of course, but that didn’t mean she wouldn’t retaliate out of principle. I wasn’t really in any position to get out of arm’s reach quickly enough, nor did I have the energy to fend her off.

“Pretty sure that’s still blackmail,” I said instead.

“So you don’t want me to do it then?”

Susan delivered the sentence in a completely neutral tone, but I could sense that this was one of those moments where she was giving me the decision. If I firmly told her not to proceed, she wouldn’t. She’d be disappointed though, she had clearly put enough thought into this plan that it wasn’t just a spur of the moment thing.

“I… just be careful okay?” I said. “I don’t want anybody getting hurt over this.”

“Don’t worry, I’m not actually going to threaten her or anything. Everything’ll work out.”

My indirect approval was enough for Susan who seemed happy that I wasn’t shutting her down. As she snuggled up to me I wondered if that was truly the right decision on my part, even though I also realized it might not matter. As much as I tried to keep her out of trouble, it was just part of who she was and I didn’t want to take that away from her even if it meant leaving my comfort zone sometimes.

****

A couple days later Susan invited Sherin over, presumably to bring her in on the plan. My sister hadn’t even filled me in on all the details, but she assured me she’d been working on it and she seemed confident everything would work out. I was skeptical that it would be as easy as she thought it would be, on the other hand I didn’t have all the information that she did.

After a little while locked in her room with Sherin, Susan came to find me with a grin on her face.

“Did it go well? I take it?” I said.

“I think she’s in, except she hasn’t technically said yes yet,” Susan said, waving it off as though it were a minor detail. “She might need some convincing.”

“Dare I ask what kind of convincing?”

“Nothing you wouldn’t enjoy. Come on, I’m gonna need you too.”

I let Susan drag me to her room where Sherin was idly toying with my sister’s computer. She looked a little surprised to see me come in as well, but not bothered by it.

“Alright, let’s get some things straightened out,” Susan said, gesturing for me to sit down on her bed. “First off, Sherin, you know about me and Ben already and I appreciate you being okay with it. It makes things a lot easier not having to hide it from you.”

“Hey, it’s not like it’s my job to police your life,” Sherin said with a shrug. “And you guys seem happy enough.”

“Mm-hm,” Susan agreed, sitting down in my lap.

I wrapped my arms around my sister’s waist as she leaned toward me. She was watching Sherin closely and I wondered if she was trying to get some kind of reaction.

“So anyway, explain to me why exactly you feel the need to have sex in the middle of school,” Sherin said, sticking to the topic at hand rather than taking the bait.

“Because it’s something I’ve wanted to do for a while but never really had a chance, and now I’m running out of time. It wouldn’t count if I did it when I wasn’t a student anymore. It’d hardly even be worth it,” Susan said.

“So this is what, some kind of fantasy for you? Because I’m not sure it’s really worth the risk,” Sherin said.

“Maybe, but what’s the point of going through life not doing the things you want to do?”

Sherin didn’t look like she was going to argue that point, but she didn’t seem completely convinced either. Unlike me she probably wouldn’t go along with whatever Susan wanted just because she was asked.

“Come on,” Susan prodded. “It’ll be fun and you’ll always be able to look back and remember that you helped your friend do something stupid and completely awesome,” Susan said. “Everyone needs memories like that. And besides, if we need to I’m sure we can make it worth your while.”

Sherin raised an eyebrow and seemed intrigued by the offer at the very least. Like me, she was probably wondering what exactly my sister meant by that.

“After all,” Susan continued, “you’ve got access to a brother and sister who are way too naughty for their own good, and we’d owe you. You can’t tell me there’s no temptation there somewhere.”

Without waiting for a response my sister turned and kissed me, pulling my head toward her slightly so she could reach. She held the kiss longer than strictly necessary to make her point and by the end I was getting short of breath.

I didn’t know whether my sister intended to play more toward Sherin’s feelings for me, whatever they might be at this point, or some perverse fascination in a sibling relationship that had gone far, far off course. Personally if I were in Sherin’s position I was confident I wouldn’t immediately dismiss the idea due to lack of interest.

It seemed that our display had at least made Sherin think. She chewed on her lip seemingly considering the possibilities, shifting her gaze rapidly between Susan and me. My sister noticed it too and that faint upward curve of her lips that signified triumph appeared on her face.

“So if I wanted you two to do something…” Sherin said carefully.

“We’d probably do it,” Susan finished.

I wasn’t all that surprised that I didn’t get a say in the matter. Susan would just assume that I’d be okay with it and the fact that my cock was starting to poke into her butt would give me away if I tried to protest. Not that I was planning an escape just yet; it wasn’t exactly the worst thing in the world to be stuck in a room with the two girls I’d most recently done something sexual with, even if I didn’t know what was coming.

Sherin, with a little more consideration for my feelings, made eye contact with me before speaking again. I shrugged slightly and gave a slight nod, hopefully enough to convey that I was not an entirely unwilling participant in the proceedings.

“What about, like, if I watched you get Ben off?” Sherin suggested.

“Any particular way, do you just want to see me playing with his cock?” Susan said. “You just want to make sure we’re actually doing what you think we are? ‘Cause we definitely are.”

Susan didn’t really look like she cared one way or the other what her friend’s motivations were and happily hopped off my lap onto the floor. She wasted no time undoing the front of my pants and fishing out my cock, encircling it with her fingers and stroking it gently.

“Fuck, you’re really gonna…” Sherin started. “I mean, I thought you were but I didn’t really… I don’t know, it’s just kind of weird to see for real.”

“It’s not really the sort of thing you see every day is it?” Susan agreed. “Which is good because it’s so much hotter when it has to be a secret.”

“Yeah, what would be the fun of having sex with your brother if everyone was doing it?” I added with only a small amount of sarcasm.

Susan rolled her eyes but leaned in to suck the head of my cock into her mouth instead of responding. Between her hand and having someone watching us I’d gotten hard fairly quickly and it felt good to have my sister start getting serious about it instead of just playing with me.

The fact that not too long ago the girls’ positions had been reversed wasn’t lost on me, Susan having seen Sherin giving me a blowjob in my room. I hoped there wouldn’t be too much awkwardness arising from that, but Sherin certainly didn’t seem too put out. Especially since she was the one who said she wanted to see it.

When it came down to it, I couldn’t figure out precisely what Sherin was thinking. Her face wasn’t giving me enough information to decide whether she was merely curious or whether she was actually enjoying what she saw on some perverse level. It was a very typical guy thing, but I couldn’t help wondering what might happen if she decided she really liked watching us. There was some fantasy material there if I chose to take it.

“Okay, you’re right. This is pretty hot,” Sherin said eventually.

Susan had my cock filling her mouth, but still managed a muffled sound of agreement. As my attention was drawn back to my sister I noticed that her hand was down the front of her pants, somehow I’d failed to catch that she was getting herself off at the same time as me.

Sherin still wasn’t openly masturbating or anything overt, but when I looked for it I saw that she was fidgeting in her chair and squeezing her legs together every now and then. She was definitely getting horny watching us even if she wasn’t comfortable enough to do something about it.

I returned my attention to Susan who continued to suck my cock and bring me closer to orgasm while simultaneously getting herself off. Since neither of her hands were free I brushed some of her hair back out of her face where it had fallen, tucking it behind her ear. She looked up at me and deliberately took me deeper on the next couple down strokes, letting my cock go far enough for me to feel the back of her throat before pulling away again.