A Different Reflection

A Different Reflection

Tags: Twins, Twincest, CAIS, intersex, siblings, dna

Standard Disclaimer

This is a work of fiction for adults. If you are not an adult, wait.

If you don't like fiction for adults, that's your choice.

All characters are above the age of 18.

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Nick walked into the apartment he shares with his twin sister and put his stuff down from work. She came out of the kitchen wearing sweat shorts and a t-shift that hugged her body.

"Hey little bro." she grinned. "I need help with the research project. Do you want to do Mario Kart shots first, then we can talk about it over pizza?" Nicole asked.

Nick nodded. "Mario Kart shots sound great. Be right back." he went to his room and changed into comfortable clothes: light sweats and a t-shirt. Going back to the living room was starting the game.

"Alright. A mini shot each lap and a full shot for the winner." Nicole said getting comfy on the couch.

"Same as the other times." Nick settled into the bean-bag chair. "You're going down."

She poured out ten half-shots and one full on the table between them. "Ha! You've never come close. We're doing Moo Farm first. Pick your Kart and player."

On the third lap, Nicole was in position 2 and Nick in 7. "You'll never catch me little bro." she gloated. "Might as well finish your shots now."

Towards the fifth lap, "Loving it back there sis?" Nick asked. "Shame you caught that banana."

He had his celebration shot watching his Kart take a victory lap and Nicole crossing the finish line.

"I needed that Mystery box on the third lap," she groused standing up. "I'll put the pizza in the oven."

She walked past him, her hips about eye-level. He playfully swatted her leg. "Thanks sis!" and went back to watching the game re-cap.

"Hey! Here's where you slid past the box off the side," he call over.

She looked at the screen. "You're the one who threw the banana, jerk!" she said putting the pizza on a tray and sliding the oven shut.

"Another round." he said pouring the half and full shots. "Maybe your luck will improve."

She sat back down putting her legs around his arms and pulling him forward. "See if you can play with the leg-lock handicap."

He settled back, reaching around her legs. "Like we're 8 years old again." he reached his arm around, grabbed his controller and started the game. "Rainbow Road or Bowser?"

"Bowser," she replied. "Rainbow Road is pretty but not as interesting."

After the first lap, "Hey with your legs holding me, I can't get my shot," he said. "I'll pop them at the end."

She pulled him closer to the couch, his head inches from her between her legs. "Deal, loser."

After the third lap, she was in first and he was dead last. "Can't play with your arms back?" she asked.

"Kinda hard, but eat shell!" as he launched one of his orbiting shells up the track. It bounced along the walls and scored a hit. Her Kart went spinning as she fell to fourth place.

"Still ahead of you little bro," she mocked. "Banana time!" Her character tossed a banana to the track on the narrow portion of the road. He hit it and spun.

"Dammit! No fair!" he claimed.

Towards the end of the final lap, she's in second and he's in fourth. As they jockey for final position, the timer went off. "Pizza's done!" she exclaimed. "I cooked, you have to get."

"Finish the game first," he replied passing to third place.

"I don't want my pizza burnt." she said pulling his arms closer. "And the timer beeps are annoying."

"No fair!" his Kart fell back to fourth as he couldn't use both hands. "And why are you so hot back there?" he asked with his head between her legs, pressing towards he crotch.

She quickly released his arms. Her Kart crossed the finish line just ahead of his.

She took her victory shot as he got up to pull the pizza from the oven. He flexed his shoulders and called back, "I could have broken out of the leg hold you know." He put the pizza on the stove to rest. "Tie breaker." he announced.

"Sounds good. Don't forget your shots." she pointed to the table.

He groaned as he downed the 5 half-shots. He refilled the glasses and settled into the beanbag chair. He pulled it to the side away from her. "Spoil-sport." she pouted.

"You good with Snowland?" she asked. He nodded and they selected Karts and characters.

Around the second lap, she said "I think the shots are getting to me" and slid off the course.

"Yep. Same. Pizza will taste good." as he pulls into second place. "You're in fifth in case you didn't know."

They finished the race and he took his victory shot. "Alright, I'll get the pizza. Movie?" he asked.

"We can get the pizza, but I do need to ask you some questions for class."

As he brought the cut pizza back, "Sure, what's up with your research study?" he asked.

"We're twins, right?" she began.

"Yes." he replied. "Been that way our whole lives. You were born first and won't let me forget." he said with a grin. "Same brown hair. Same light brown eyes. Me boy, you girl. Separate eggs if I recall my bio right."

She took a bite of pizza and thought a second before continuing. "After college, you went off to work putting your Mechanical Engineering degree to use. I'm the bio whiz and currently working as a research assistant with Dr Simpson for my PhD."

"Yep. You're studying something about reproduction if I understood right." he said around a mouthful of pizza.

"Something like that." she answered shifting closer to him. "It's a little more complicated. And honestly, personal."

"Nic," he began, "we've both had shots on an empty stomach. Thinking isn't going to go well for either of us. What are you trying to say?"

"I have the condition I've been studying." she said looking down. She looked up at him. "You should too and we want to figure out why you're not affected."

"What?" he asked. "Is that why you asked me for a mouth swab the other day?"

"Yes." she said. "The swab was for a DNA test. Turns out we're identical or maternal twins, not fraternal."

"Back up. We're from different eggs and stuff. It's impossible for us to be from the same egg."

Nicole smiled. "You'd think, but no. I have a genetic condition called Complete Androgen Insensitivity Syndrome, or CAIS. My body rejects testosterone which is a primary androgen. The default gender is female so my body developed as female. It takes testosterone to tell the body to develop as male." She looked at him, "And since we're twins with the same DNA, you have CAIS too."

"I got about half of that, but how is that possible?" he asked. "I'm male."

"That's the Nobel question." she replied. "Which is why we want you to stop in for some tests."

"What would you need?"

"Well, blood work. After that, dunno."

Nick thought for a second. "Yes. Of course I'll help. It still doesn't make sense."

Nicole nodded. "Yeah." She stood up. "A quick physiology comparison." Gesturing, "Stand up little bro."

Nick with a buzzed wobble. "I'm taller than you with muscles and everything."

Nicole walked over. "Yes. I'm 5-ft 8-inches, that's around the 95th percentile. You're 6-ft 1-inch which is just over 95th percentile. CAIS women tend to be taller than average; you're just above average for men" She reached out to his arms. "Muscles. Yes."

He looked at her feeling his arm. "Nic, you know I go to the gym three times a week. You should come too. Put some muscle on you."

She continued feeling up his arm to his chest. "Wouldn't matter. People with CAIS have trouble putting on muscle." She stopped and turned sideways. "One of the hallmarks of CAIS is a well defined female form."

She raised her arms up and straightened her back, pushing her chest out. "See, my breasts are well developed." She lowered her arms to her hips. "Hips are wide and inviting." She turned to him and struck a pose.

"Sis, you're kinda freaking me out. Yes, you're hot. Friends of mine have said it many times. But we're siblings."

She approached him, placing her hands on his chest. "You have chest hair. I've seen it." She rubbed his chest. "Pectoral muscles too."

"Sis, yes. I have chest hair." he backed up. "You have body hair too."

"Oh, no. I don't have body hair." she pulled down her sweats and underwear in one motion. "See, no hair."

"Nic, you're drunk. You shave." he said averting his eyes.

"Maybe and No." she dropped her pants all the way down. "I can't grow body hair. It's part of CAIS." she stepped forward, out of her pants. "Meanwhile do you?" and she reached to his pants.

"Nic. Stop." he said backing up. "Yes, I have hair on my privates."

"Prove it." she challenged.

"Why?" he retorted. "Do mom and dad know about this condition?"

"We found out when I was 12." she said stepping forward taking off her shirt and lifting her arms over her hourglass figure. "See no hair in the pits either."

"Why are you undressing?" Nick asked.

"Because I want you to undress too." Nicole said. She looked down, slightly dejected. "I want to know what could have been. We're twins, fully DNA compatible. Why did you turn out male and I'm female."

"I don't know." Nick shrugged. He considered for a few seconds. "If if means this much to you, I'll undress this once and during the exam. No touching."

"Ok", she nodded looking up.

He took his shirt off and with a glance at his sister, dropped his sweatpants leaving his underwear on. "There?"

"Nu-uh." she shook her head. "Full. Like me." she twirled jiggling her breasts.

With a sigh he lowered his underwear. "Oh." Nicole breathed. She took a quick step forward and grabbed his penis. "Oh."

"Hey!" Nick said. "No touching."

Still holding his penis, "Did you know that technically my clit is about the same tissue as this? Testosterone and other hormones around puberty take what you were born with to give.. this" and she slowly stroked it.

"Nic," he began. "No touching. Alright. We don't want to make this weird." He tried to take a step back but she held firm.

"And these," she said cupping his balls. "Same hormones around puberty cause them to start making testosterone by the buckets. And estrogen."

He stood there with his sister holding his cock and balls. "Sis, you're making this weird."

"This feels good, right?" she asked.

"Yeah." he said. "We've both been drinking. I don't think this is a good idea."

"I'd have this too, if my body didn't reject testosterone." she mused still stroking his cock. She released his testicles and started rubbing his chest. "Muscles too."

"Is this how you're getting a sperm sample?" he asked teasing.

She continued stroking his hardening cock. "Lets head to my room."

"Nic, I don't think this is a good idea. What do you want to do in there?"

"Since I found out that we're identical, I've been curious what I'd look like. And figured when I told you, you'd be curious too." she continued to hold his cock. Looking up at him, "Think about it. We are genetically the same. If we had developed normally, we'd look exactly the same except for any injuries. But something happened in utero." Her thumb stroked the back of his cock-head.

"Sis, I love you. If this will help with your research, ok. But please," and he removed her hand from his cock, "stop that."

She took his hand and led him to her room.

"All right little bro, lets compare." He sat on her bed while she held up her breasts in front of him. "These are 38 C. Past boyfriends have described them as 'perky'. From what's I've read in literature and online they don't have as much sag as others."

"Yes, very nice." said Nick.

"Feel to compare. It's for science." Nicole asked bouncing them up and down.

"I can see they're perky," he said. "If you're looking for a dollar, I'm out."

"No," she smirked. "I'm not going to pole dance for you. Your breast tissue is minimal." as she reached over. "When you hit the gym, how much time do you spend doing chest?"

She felt the firm definition of his chest, tracing the lines.

"Not as much as I should. They don't seem to need it."

"That's a good data point." she said circling his nipples. "Interesting, our nipples look the same but my areola are slightly larger. See?" she put her breast directly to his face.

"Uh. Nic," he started. "What do you want to get out of this?"

She paused, pulling his breasts from his face. "After looking at the test results, it got me thinking. Being the same, you're me in a male body; I'm you in a female body. Then I realized I was attracted to you. I mean, I love you as a brother. But," she took a breath, "I also want to physically be with you."

Nick paused to consider. "To be honest, you and I are pretty attractive." he confessed. "I took a lot of ribbing from friends in high school that I was lucky to be living with such a gorgeous woman." Reaching out to her breasts, he continued. "I agreed with them then, and agree with them now. I am lucky to be living with an absolutely gorgeous woman."

Pulling his hands back, "Who's also my sister. Having a physical relationship with you wouldn't be in our best interest."

She pulled his head to look up at him. "Says who. Right now I'm looking to understand our physical differences. We can stop when we want. I'm not asking an exclusive relationship. You said you want kids, I can't. I look forward to being an aunt. But, will you allow tonight to happen? And we can re-evaluate in the morning."

Looking into her eyes, he saw himself. Slightly lighter skin tone, a lot better complexion, but the same nose, eyes and color, cheek bones, and lips. He knew every shape of her face without touching it, because it's his face.

"Yes. Tonight only." He chuckled, "Otherwise I'd get no peace because you'd be the pestering older sister I know and love." Settling back on the bed. "Where would you like to start?"

Her finger on her lips, she considered and pointed to his chest. "Lets complete our comparative exam on breast tissue and muscular development." Climbing on the bed next to Nick, she traced his chest. "The pectoral muscles are well defined for Patient X. In comparison to Patient Y," she picked up his hand and placed it on her breast. "Please give your analysis on Patent Y."

"Nicole, what are we doing?"

"Comparison. How do my breasts feel?"

"... Good?"

"Nick," she moved his hand around, squeezing her breasts. "Are they firm? Saggy? Science needs to know."

"Oh. Uh, firm. Very nice." he paused. "No sag, and the nipple is, uh, prominent. Is that the right term?"

"Very good. My nipples are erect as are yours." She reached down and twisted one to his discomfort. "How do they taste?"

He leaned up, placing his mouth over a nipple. "Pretty good. New body wash?"

"Yes, apple. Glad you noticed." She leaned over placing her mouth on his nipple. With her mouth she pulled it, and with her hand massaged the other pec.

Nick caught on and began rubbing her breasts as she lay over him. Caressing and tracing her areola with his fingers, he massaged her breasts.

She increased her teasing of his nipple, her mouth led to her tongue swirling around the rough edges of the erect nipple and onto his nipple. Her teeth rubbed against the edges of skin, scraping on the nipple itself, then teasing it into her mouth.

He moaned and began twisting her breasts, paying attention to the rigidness while caressing the soft flesh holding them.

She stopped and sat up. He lost his grip and motivation, and opened his eyes. "You stopped." he accused.

"Yes. We determined that while you have excellent muscular structure, mine are superior tactilely. I must note, clinically of course, that you do have a higher sensitivity. I'll take advantage of that." as she moved her hair out of the way.

"Big words hurt small man brain. What?" he leaned back on his elbows.

"Mine feel better but yours are more sensitive." she translated. "How does this feel?" she asked reaching for his penis. Her hand grabbed under the head. "Looks like you were waiting." She felt along his chest. "A moderate amount of chest hair."

He shifted and lay back as she slowly squeezed and released. "You got this pretty thing." She looked at his penis, "And I, something else." Looking at his face she began to slowly stroke it. "Ah, self lubricating too. That's important." Her hand pulled some pre-cum from his slit and rubbed that down the shaft. Still looking at his face. "To think for a difference in chemicals, at one critical point, we'd each have one."

Rubbing her thumb on the ridge under his glans, she moved her other hand between his nipples. Flicking each with a nail. "Feel good little bro?"

He nodded and moved with her hands. The rubbing on his cock moving his hips, and his chest flexing with her each sharp motion.

She abruptly stopped. One hand still on his cock, just under the glans. The other resting on his sternum.

His eyes opened and his hand reached over to her. First along her hips. Slowly down the top of her leg "So smooth" he thought, then between her legs.

The first thing he noticed was the presence of no hair. No stubble. Only smooth skin leading to... a gentle, smooth, and soft mound. His fingers felt around the mound to the warmest spot.

"Little bro.." she said moving to her side. "You were always good with taking turns."

"You talk too much, big sis." He rolled over making room. She slid onto her back. "Lets see what you keep talking about."

His fingers moved around her pubic mound. "You say you don't need to shave." She nodded. "Interesting." He felt the slit at the top. "This feels normal." His fingers touched into the slit to the hood as her breath quickened. "Nothing out of the ordinary here."

Leaning on his elbow, with one hand in the top of her sex, he reached to her breasts. Slowly rubbing a nipple, "This too seems about right." His finger reached past the clitoral hood until it found her his target - her clit. His finger just brushed causing her to have a sharp intake. "You seem to be sensitive there. And here." as he pinched her nipple.

He continued finger play on her pussy and nipple. He leaned over and sucked on the other nipple. Nicole moaned and arched her upper back. Around a nipple he commented, "Like that?" and he redoubled his efforts on all three fronts.

She groaned as he pulled his fingers from her crotch. "I'm not the only one who's self lubricating it seems." He licked his fingers and put them to her mouth. She also licked, pulling his fingers in.

"Nice." he commented as she sucked his finger tips dry. He removed his fingers and she ran her tongue across her lips.

He leaned in a gently kissed her. "You taste like you. Or if what you are saying is true, you taste like us."

She grinned. "You're starting to get it."

He lazily drifted his hand from her crotch, down her leg and back up. "You have an amazing body." he commented. His hand moved along her flat stomach, up to her breasts, and up her neck. "It's little wonder that my friends always wanted to come over."

"Mine too" she said, her hand moving along his reclining torso. "Do you remember Patty? She had the hots for you in 11th grade."

"Patty with the braces? Yeah. She was alright." he circled a nipple. "So what's with this genetic thing you're working that affects both of us?"

"Well, I'm confirmed to have CAIS. I explained that to you. The 'C' mean Complete. I wanted to check if you have a variant called PAIS, where the 'P' means Partial." She held his cock. "Based on this and your breast tissue and chest hair, I'd say you don't have PAIS either. So you may have MAIS." She looked at him, "Or something completely different."

"Mays?" he asked

"MAIS. Mild Androgen Insensitivity Syndrome. These are all based on genes so I'd expect with CAIS markers you'd have CAIS like me."

"How do we find out?"

"One of the keys with MAIS is infertility or low fertility. A sperm sample will be needed." She massaged his cock. "We can do a formal test later."

"An informal test now is what you're thinking." he grinned at her. He rubbed her mons, pressing in. She gave a slight moan gripping his cock.

With her other hand, she stopped his pressing. "We need to talk about something first."

He paused. "I can run to the store and get condoms. I'd never seen you with a pill-pack, but I figured it wasn't my place to ask."

She smiled. "No, that's not it. I can't get pregnant. That's an affect of CAIS."

Sitting up, "I have a blind or dead-end vagina." she held up her hand as he opened his mouth. "In my top drawer is a set of vaginal dilators. They are medical devices allowing me to have sex." She reached out to his penis. "You're bigger than I expected and the size that I normally use."

"Big sis, I've seen your vibrators."

"I have a vibrator. You saw the dilators." With a sigh, "Behind the curtains my vagina is different. Think of it as a pocket. There's no uterus to pull it in, and without being stretched it'll shorten. The dilators are there to keep the pocket formed to take a penis."

"How deep is this pocket?"

"Without the dilators, about 3 inches. I've had it as deep as 6 to 7 inches but it got uncomfortable maintaining it. Right now I can comfortably handle 5 inches. Maybe 6. You," as she looked down at his stiff member, "are easily into the 6 inch range."

"Maybe if you relax?" he said sliding down her. He rested his chin on her pubic bone with a smile and moved down between her legs. Lifting by her butt-cheeks, he gently placed his tongue on the top of her folds. Feeling with his tongue, it moved between the moist flesh and found her button.

With a shudder she moved down the bed to him. "Where'd you learn that?"

"Katie in freshman year." he replied while darting his tongue out. "She said she never had an orgasm from a dick, so she got hers first." With a nibble to her labia, "She was very specific." His tongue gently ran up where he nibbled as he watched over her hips.

Nick continued for minutes watching his sister writhe. He timed his tongue to meet her hips as they moved. When he couldn't distinguish between her taste and his own saliva, he moved from her pussy up her puffy mons and joined her back on the bed. His fingers slid into the place his mouth had occupied and he teased his sister's clit. First one finger circling. Then moving up and down, back and forth, adjusting the pressure based on her movements.

Nicole involuntary moved, solely based on her brother's ministrations. She attempted to contentiously move, then he would do something causing her to reflexively lay back.

Laying next to her, propped on an elbow, he grabbed a nipple in his mouth. His lips on the edges of the nipple and his teeth gently biting. Her eyes rolled back as she neared orgasm.

"Don't tease," she struggled saying, "little brother."

Grinning with her breast in his mouth, his hand cupped the other breast. Holding the nipple between his teeth, "I never forgave your for losing my best pokemon cards." He twisted her nipple as his fingers pinched her clit and pulled.

Then he stopped.

Sitting up with his hands by his side he watched his sister. Her eyes popped open. "Nick! I was close!" he smacked his leg.

"I know sis." as he lowered his head to her breast. "If I didn't tease, I wouldn't be a good brother would I?" he pulled her erect nipple back into his mouth. Pinching it with his teeth, "Lay back and I'll make you forget what happened to your Barbies."

With a smile, she closed her eyes, "You better."

For the next few minutes, he fondled and teased her breasts. His fingers explored her pussy, marveling at the lack of hair. Curiously he explored in her with his fingers. He first put his index finger in, finding it tighter than other girls he's been with. He continued working on her breasts, as her opening loosened further.

He was able to insert his middle finger into her vaginal hole. Probing, he gently moved in and out, his thumb rotating her clit with gentle pressure. When his finger stopped all the way in he began massaging in her, and along her opening.

She began moving with him again, moaning as his finger went in and out. He bit hard on her nipple to watch her eyes sharply open, then close again. His other hand softly went up and down her body from her breasts to her hips. He admired that her waist wasn't a dramatic angle, but soft as a gentle curve under her breasts.

He stopped mouthing her breast, continuing to fuck her with his fingers. She responded with him. He sped up, so did she. He slowed down, she matched. He watched her breasts, pink orbs sitting on her chest, move. Stroking a breast made her slow down as she enjoyed the sensation on her sensitive skin.

He began rotating his finger in her pussy. Her breathing sped up. His other fingers ran up and down her folds and his thumb struck her clit with force. The breathing turned into passionate moans and she reached down to grab his hand. She directed his motions as her hips moved around.

With a final intake she pulled her hips up, pushing his hand further into her sex, jamming his thumb along her sex button, she paused and stiffened. "Oh fuuuuuuuuuu..." Her hips bucked against his hand, grinding his thumb.

"Oh fu..... ck!" She let go of his hand and lay back. Orgasmic tremors racking her body. He felt her legs and pelvic muscles working against his hand. She continued to work on his finger for a few minutes.

He stroked the folds around her vaginal opening as she opened her eyes. "That feels nice, little bro. But it's not necessary." A quick twitch, "Ok, that was good."

He stopped and left his finger in her pussy, resting it. He bent down and kissed her on the lips and sat back up. She looked up at him "I think that's the first time we've kissed like that."

He smiled and bent down again. This time with more force. Her tongue slid into his mouth and his back to hers. His finger movements in her vagina matching his tongue action. She moaned again, pulling her legs up as she shook with a smaller orgasm.

She pulled his hand out as he sat up. "Maybe one Barbie." Sitting up, she pushed on his chest, forcing him down on his back.

She grabbed his semi-erect penis and knelt down next to him. "Lets get this back to life." she said slowly rubbing it. "And your chest needs attention again." One hand around his cock, and another caressing his chest, his penis stiffened. "Oh look, you're leaking again."

From his vantage point, he looked over and saw her grinning. "What are you going to do about it?" he inquired.

"This." She let go of his penis, placing the other hand on his chest, she straddled him. Lining his solid member up to her vagina, she slowly lowered her pussy down to meet his cock-head.

Looking right at him, she rubbed his cock-head between her folds. He resisted the urge to thrust straight up. She gently lowered down so just the very end of his penis was at her opening. Moving back and forth, her labia folds rubbing on the glans.

Closing her eyes, she lined up his penis and forcefully lowered down. The tip of his penis penetrated as she took a breath. "You loosened me up, little bro." Opening her eyes, she saw him looking at her face with wonderment and love. Leaning in, she kissed him on the forehead, his nose, then on his lips. Nicole lowered herself, feeling him enter her. As she got lower, she slowed down until she stopped.

"What's that?" Nick asked.

"The back wall of the pocket." she looked down at his shaft. "You have about a half-inch left." She wiggled around. "Lets try to flex that."

She raised up, causing Nick to moan. "Feel good?" she teased. He could only nod. She slowly lowered back down until he hit the spot again. "I think that was deeper." She tried more times, each try managed to get more of Nick's penis in. Finally she was resting on his hips.

"I'm glad my body remembered." she said shifting her weight. "I wasn't sure for a minute."

"You're not hurt?" Nick asked concerned.

"No." she said shifting. "It's skin. I have to be careful, so no thrusting. But it stretched."

Her hands on his chest, with her fingers on his nipples, she slowly lifted up and back down. As she started the motion her fingers twisted and played with his chest. "You have nice chest hair."

"Thank you. I do some man-scaping, but not a lot." he looked down and saw her palms sliding over it. He reached up to her breasts. He squeezed and teased around her nipples as she did the same to him. She pulled up and slid back down. "We fit together nicely" she said through half-closed eyes.

He could only nod as his own orgasm built. The tightness of her pussy and her rubbing his head against the end of her vaginal pocket was causing his breath to get short.

"Nic?" he asked. "You sure you can't get pregnant?" he looked up at her. "Because I'm real close."

Looking down, "Positive."

"Ok." he closed his eyes as he felt his balls tighten in. "I'll try not to push."

He felt her lift off slightly, "It's ok."

He nodded and exploded. His hips jerked up as he came. He could feel each pulse from his cock inside. Nicole gasped as she felt his dick pulsing. His hips met hers and she rode him up. She could feel him filling her. He could feel his own cum flooding back along his cock and down the shaft.

"I - I think I filled you?" he stammered mid-thrust on the fourth orgasm.

She nodded with her eyes closed, thinking "full feels good".

His last orgasm subsided and he relaxed on the bed. She settled back down, but held herself just above him. His cum pooled around his penis, still in her. It was dropping down onto his crotch, mixing in his hairs.

She continued lifting and lowering, forcing more of his spunk out of her. This had the side-effect of causing him to have smaller orgasms on his sensitive cock. "Nic," he pleaded.

"Sorry." she said stopping. "It felt good."

They sat there for a few minutes. Her hands on his chest, his hands on hers. She impaled on him. Finally she spoke up, "I need to get cleaned up." She sat up freeing his cock and a final clump of him fell out above his penis.

She walked into her bathroom and closed the door. He lay there, with his hands crossed on his chest. He heard water running, and a flushing sound.

She came out. "Sorry about that. If I don't clean it out, it can get gross."

"Big sis, I know I was hesitant when you suggested this." He turned on his side to her. "And you said you wanted to know something. I'm still lost on what you were looking for and if you found it."

She sat on the bed next to him. "I think I may have found it." She kissed his forehead. "You and I are identical twins." She picked up his flagging cock. "Sometime during development my DNA." She paused. "Our DNA made me a girl, and somehow you were left to be a boy."

He nodded.

"Since we are identical we should have both developed the same. I wanted to see what I would have looked like if I had developed as a boy. How it things would feel as a boy. And," she paused, "part of me wanted you to know what you could have been. We're reflections of each other, only different genders."

He nodded. "How would our DNA do this. I thought DNA made a boy or a girl and that's that."

"It's not so simple." She rubbed his penis. "XY chromosomes should develop to be male, but I'm proof that doesn't happen. And there's people with XXY and XYY chromosomes. Biology is weird sometimes."

He cupped her breast. "So you want to bring me in as a baseline for our DNA, to see where your development went wrong?"

Nicole laughed. She looked at her brother and laughed again. "What?" he asked.

"Nick. You're the outlier." she said with a grin. "Our DNA says to ignore androgens. Not respond to them at all." Holding his penis she continued, "My body did that. Your body, responded to the androgens. See?" she said tugging at his penis. "This is because your body responded to testosterone and made you male when the DNA said it shouldn't."

Stroking his penis thoughtfully, "I will say, this is a very nice penis." She bent down to bring it to eye level, "a little soiled and used, but very pleasant."

He rubbed her breasts with his hand, "These are nice too. Interesting to think I could have had a matching set."

She let go of his penis. "How are you sure you don't can't get pregnant?" he asked still holding her breast.

"I have the blind vagina" she pointed around her navel. "Nothing above that except some testes. No uterus and no ovaries means no kids."

Nick sat up. "You have what?"

Nicole gave a small laugh. "Yep. You're not the only one with balls around here. They're checked every year to make sure they don't get cancer, which can happen. That's how I met Dr Simpson at the research university. Our pediatrician suggested mom and dad take me to him after I didn't have periods like other girls. He's the one who made the CAIS diagnosis and he's been giving me yearly cancer screenings."

He sat back. "I came home from work looking to dinner and play Mario Kart. Now I find out my sister has balls, a much better figure than me, and I'm the abnormal one." He shook his head.

"And I found out I could have been muscular and well hung, that my brother gives excellent oral and is a considerate partner." She pushed him to the other side of the bed and sat down.

Grinning, she touched his shoulder. "I'm ready for another round of Kart."

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Author note: Feedback is welcome!