I live in a world where there is a curious rule: on their 18th birthday, all boys must sleep with their mothers. This is an ancient tradition that is still respected today.
My name is Vincent, and today I am 18 years old. I live with my parents Frank and Maggie and my sister Sarah. I'm a bit nervous because tonight I know what's going to happen, I'm going to have to make love to my mother. I have to say that I'm lucky, at 46, she's still gorgeous: a beautiful face, long brown hair and a sexy curvy body. She's a little shorter than me and most importantly she's pregnant with twins. My 16 year old younger sister and I were very surprised when our parents told us the news, we would soon have a little brother and sister.
It's the end of June, school is almost over. It's hot and sunny, and tonight my father is going to make us a great barbecue to make me happy. But I'm stressed, I'm a virgin and I'm nervous about sleeping with my pregnant mother. When I get to school, my two best friends, Alex and Tom accost me.
"So today you're a man, happy birthday!" says Tom.
"Finally 18!" says Alex, patting me on the back.
Alex and Tom are already 18, and they've already had their night with their mother.
"Thanks guys. This is so cool. I'll finally be able to drink and go out clubbing." I say this hoping not to bring up the taboo subject. Alex and Tom look at me with wide grins. "What?!" i said.
"Don't pretend, tonight you're going to bang your mum," Alex said. He had been lucky enough to be able to make love to his mom without a condom and he was very open about it.
"We all have to go through this," Tom added. "But don't worry I'm sure you'll like it." Tom had a difficult relationship with his mum and on the night of his 18th birthday he had made up with her in bed.
"Yeah, plus your mum's knocked up, so I'm sure she'll let you fuck her unprotected," Alex said as if he was the one who was going to enjoy it.
"Well guys can we stop talking about this, it's making me uncomfortable," I say as I try to push away the images of my mother that keep popping into my mind.
All day I felt a kind of tension as the fateful moment approached. After class, I walked home in the bright summer sunshine. As I reached the front door of my house, I took a deep breath and pushed it open.
"Happy birthday!" my sister jumped on me and hugged me and kissed my cheek.
"Thank you. Thank you!" I said as I put her down. My father came in from the living room.
"Ahh, our young man is home. I'll get dinner ready." My father walked by me. "You come and help me with the barbecue, we need to talk," he said, winking at me.
"I'll meet you there."
"Your mother is in the kitchen making the cake, you should go and see her." My father headed out into the garden to light the fire.
Gathering my courage, I head for the kitchen. Mum is there, beautiful and pregnant: she is wearing a long dark blue summer dress, perfectly marking her huge belly, she is entering her ninth month of pregnancy. I can't help but stare at her generous breasts and pretty ass. She is making what I imagine to be a delicious strawberry cake for dessert tonight.
"Ah, sweetheart," she says, noticing my presence. She comes over to me and gives me a soft kiss on the cheek. "Happy birthday."
"Thank you, Mom."
She put her hand on my shoulder and said, "If I had imagined that you would be such a beautiful young man."
"I have beautiful parents." To think that tonight I was going to lose my virginity to her. I looked down at her giant belly. Mum put her hand on it and then grinned at me.
"Vincent! Are you coming to help me?"
"I think your father needs you." She turned around. The sound of her little sandals on the tiles drew my eyes to her delicious legs.
I head for the garden when Sarah runs up to me and grabs my arm.
"Good luck tonight brother" she said with a friendly smile. My sister was a great girl and we always got along very well. I don't say anything and just smile at her. She must sense that I am nervous.
I go to the garden, my father barbecuing.
"Come on Vincent, I need to talk to you," he says as he lights the fire. I get closer. "So how do you feel?"
"I don't know, happy but a little..."
"Worried? Ha don't worry, it's still a bit special being 18. I remember mine with your grandmother. I was as nervous as you were, but it'll be fine, and tonight you'll be a man."
"Yeah, I guess so." I feel my cheeks turn red.
"You'll see, your mother will take good care of you, I'm sure." my father pats me hard on the shoulder.
"Go get me the meat and then we can eat."
2 hours later...
I am at the table with my family, I have already blown out the candles, eaten the meal and the dessert. But there is still one thing to do: receive my present. My sister tells my parents about her day and I am lost in my thoughts, I take a quick look at my mother, her condition barely allows her to sit normally on the chair. I raise my head to meet her eyes.
"Is something wrong, honey?" she says, putting her hand on mine.
"It's been a great night, but I'm not sure what's going to happen tonight," I hope mum will reassure me, I've never been so stressed in my life.
"It's all right, Vincent, you know, every boy your age goes through this, it's a mother's duty."
My father laughed loudly at what my sister had said about a joke a friend had played on her in high school.
"Frank?" Mom cleared her throat. "I think it's time."
My father and sister looked at us in awkward silence for a few seconds.
"Oh yes, it's time. Don't worry, I'll sleep on the sofa," he said.
Mum gets up and waves me off. I follow her leaving my father and sister in the dining room. Mum takes the stairs, I notice her lovely buttocks and legs, I wonder how she manages to move so gracefully so close to giving birth. Once upstairs, Mom leads me to the conjugal room.
"Sit down on the bed and get comfortable, I need some time to get ready," she says gently as she walks to the dressing room.
I sit on the edge of the bed. My hands and legs are shaking with excitement, I can't believe this is happening, I'm actually going to make love to my mother. I know it's only going to happen once in my life, but I can't help but find this age-old tradition a bit ridiculous and outdated, it's true, nowadays a lot of boys have their first sexual encounter before they're 18.
"So I'm not too fat?" said my mother as she came out of the dressing room: she's wearing a lovely black maternity nightie, leaving her fleshy legs completely bare. She looks really sexy, even though she seems to be hiding a beach ball under her nightie.
"No, it's okay, you look great," I feel my cheeks turn red.
Mum smiles and comes to sit next to me. I then notice the cleavage that reveals her two large breasts filled with milk. I am a little intimidated by the mature woman next to me.
"You find me attractive," she says nervously.
Her beautiful, slightly greying, nicely coiffed brown hair cascading down her shoulders, her pretty face, the shape of her belly containing life, everything about her makes me think I'm really lucky to have such a voluptuous mum tonight.
"Uh, I think, I'm really lucky that you...are with me tonight." my voice trembles.
"Sweetheart, I'm your mother, and I know this is a little stressful for you, but once it's done, you'll be a man, an adult."
"All right, how do we do this?" I ask innocently. She brings her face close to mine.
"We can start by kissing." She puts her mouth on mine for a few seconds and then pulls her face back. She's probably waiting for a reaction from me. I take her face in my hands and kiss her, first just on the mouth then with my tongue. Doing a Frenchkiss with her mother is really exciting and I feel the stress in me disappear. I put one hand on her giant belly and run my hand over the fullness of her pregnancy, then place my hand on her bare leg.
We finally break the kiss.
"Wow, Mommy that's great."
"Lie down on the bed my darling." she says as she pulls her heavy breasts out of her nightie, I can't believe my eyes! Her breasts are really sublime, the size of a melon, they look quite firm.
I lie down on my back and mum comes to lie next to me on her side. She moves closer to me, putting one of her bare legs over mine, I have her big belly hidden under her nightie pressed against my sides. She presents me with her breasts. "Not too disappointed in Mummy's breasts?"
Her breasts are more than appetizing and her big nipples make me want to suck on them, "You're kidding, they're great for a woman your age."
"My age?"
"No, that's not what I meant!" I'm such an idiot to remind my mother of her age, but she laughs.
"No worries sweetheart, you know I'm aware of my age, I'm fine with it. Do you want to try it?" I nod and while bringing her chest closer to my mouth, Mom puts her hand on my shorts to feel my erect cock. But I don't have time to think about it, I have one of her big nipples right in front of my eyes. I gently bite her nipple and suddenly a stream of warm milk comes into my mouth. Mum lets out a groan of relief. "Mmm that feels good, you can empty my breasts a little, the babies won't miss it."
I look down at her pregnant belly and place my hand on it. I had never imagined that I might have a fetish for pregnant women, but the fact that my mother is one makes me feel very good. She starts rubbing my cock through the shorts and then suddenly puts her hand in to pull it out. Mum doesn't say anything, she just looks at my cock and jerks it off while I empty her big tits one after the other. She rubs her feet on mine, they are a bit cold but it's super hot. The feeling of her soft hands on my sex is great, but I can't wait to get on with it.
"Come on, Vincent." She straightens up and takes off her nightie, she's only wearing her black lace panties. My eyes are all round, my gaze fixes on my mother's figure, almost naked, her round baby orb and her heavy breasts resting on it, it's the first time I've seen a pregnant woman's naked belly so close. She sits on her lap, readjusting her beautiful hair.
I stand in front of her placing my hands on either side of her belly and kiss her on the mouth, then on the neck, working my way down to kiss her belly, which apparently has no stretch marks. Mum laughs and puts her hands on my neck as I tease her hard belly button with my tongue.
"I love you Mum, you really are the best."
"I think you're ready for the grand finale." She stands in the middle of the bed and lifts her legs up to gracefully remove her panties, she's supple for a woman in her ninth month of pregnancy with twins. And there I see her love nest, her pussy. She is clean-shaven, and the lips of her vagina look very inviting. She spreads her legs as best she can, placing the soles of her feet on the bed. "Come on, don't be shy."
I undress completely, and place myself between her two voluptuous thighs. My cock so close to the entrance of her pussy. I look up, the huge dome of pregnancy taking up most of the view, complemented by the two large teardrop shaped breasts, my mother's pretty face smiling at me.
"You just have to insert it in. Then to... I'm not going to draw you a picture, you know how it works," she said, trying to guide me.
I took my time inserting my cock inside her. The feeling of my glans entering in woman's sex for the first time will always be etched in my memory. I insert everything else at once, boy, her pussy is so tight and hot, I feel really good inside. Mum closes her eyes as my sex progresses inside her. I'm now fully embedded in her and I feel myself being arrested by something, it's her cervix which I touch with the head of my cock.
"Whaoo mum, you are so good."
Mum opens her eyes again. Amazed at how far I can reach.
"Go ahead sweetheart, you can go. Make love to me. But please don't go too fast. Wouldn't you like to induce labour?"
"Don't worry, I'll take it slow."I place my hands on her huge round belly and take in the dimensions, imagining the two babies inside, inches from my cock and ready to slide out at any moment through my mother's birth canal. I grab her thighs and slowly start to move in and out of her, each time inserting my cock fully and withdrawing it to leave only my glans in her pussy. It takes a lot of concentration and Mum lets out long sighs of pleasure. She squeezes my hips with her powerful thighs.
"Mmmm sweetheart, that's very good, you're doing very well," she says as she places one of her hands on her chest and the other on her lower belly.
"Mum, you look so beautiful, it's amazing." The feeling of being one with the woman who gave you life is the most incredible thing that can happen to a man. I let go of her thighs and lay down on top of her as best I can, feeling her large belly against me. I speed up the movement a bit, I can hear my balls hitting her ass with each push. Lying on top of her, my forearms on either side of her belly, I caress her big milky breasts. Mum continues to squeal with pleasure as she wraps her arms around my neck and her long legs around my lower back.
I feel I'm not going to last much longer, my balls preparing my cum to be expelled. I speed up the movement again, enjoying my mother's curvy body against me. With the pregnancy Mom has become a voluptuous woman.
"Oh yes Vincent, you make love to your mommy so well, your big pregnant mommy!"
"Mom, I... I can cum inside you?"
"Of course sweetheart, I can't get pregnant, cum, cum in me, fill me up, fill your pregnant mommy!"
I push into her harder and harder feeling the cum building up in my cock and finally I cum inside her, letting out a sigh of pleasure. I feel like she's cumming at the same time as me and she doesn't stop herself from screaming too. I give several dozen thrusts with my hips before I am completely exhausted.
I rest on top of her for a few seconds, feeling the babies inside kicking. I sit up to hug my mother, who looks completely exhausted too, but her face is blooming and her smile doesn't lie.
"Did I do well?"
"You did great Vincent, for a first time."
"You did great," I say as I pull out and stand next to her.
"Look at all this," Mum said as she took her hands to her pussy, my cum flowing profusely.
"Ah, I'm sorry."
"Don't be sorry, it's okay." Mum clutches me and hugs me. "I have you to myself all night."
"Mom?!"

(Continue the story that describes the rest of the night. Start the story immediately following the the prompt. The story should end when it becomes day again. They go for many more rounds of sex, each time trying out a new position or fucking eachother. Make the story very explicit. Make the story 5000 words).