Marcus, an 18 year old Doberman boy, chuckled as he watched his 12 year old brother Jay grind against the bed sheets with reckless abandon, the boy having been permanently horny since his big brother knocked him up. The child's belly was well and truly showing, though he still had several months to go. 

The older boy had woken up to the bed shaking and was at first worried, but after seeing the state the Jay was in all he could do was stare and smile. 

Jay was completely naked, his fur being soaked with sweat and the sheets had been thrown off the bed. The smaller dog boy was laying on his belly, face pushed into his pillow and legs spread out wide. His arms were out in front of him, clutching the pillow as if his life depended on it and his legs were splayed apart, giving his big brother the perfect view of his hole as his stiff clit was pressed into the mattress.

Marcus could tell Jay was trying to be quiet, but his soft moans and whines were still loud enough for the older dog to hear, and the boy was probably to lost in his pleasure to realize how much he was shaking the bed. He smiled and slowly moved behind the younger boy.

"You need some help there, baby boy?" Marcus said, making his brother jump a bit before he realized who was talking to him.

"I-I was just, ah!" Jay tried to say before the older dog reached a paw under him and started rubbing the boy's clit.

"Just what? Humping the bed like a bitch in heat? You really are a horny little slut, aren't you?" Marcus teased his brother as the boy started to hump into his hand instead of the now soaked fabric underneath him.

Jay gasped and his tongue lolled out of his mouth. He tried to reply, but all that came out were happy whimpers.

"Don't worry, I'll take care of you," Marcus said, getting onto the bed and lifting his brother's hips up. The boys belly was big already, considering his age, but not enough to keep them from getting into the position Marcus wanted.

The bigger boy's cock was already unsheathed and hard from watching his brother, and without hesitating he pressed the tapered tip of his cock against the 12 year old boy's entrance.

"H-hah, yes, please big brother! I-I want you to breed me again!" Jay begged as his brother penetrated him.

Marcus didn't say anything, he only smirked and gripped his little brother's hips tighter, pushing his entire length inside of the boy. He was plenty lubricated from playing with himself for who knows how long this morning 

Jay whined as he felt his brother's cock go all the way inside him, hitting his special spot perfectly and sending shivers through his body.

"You're already so wet for me, little brother. Fuck... I'm so glad mom and dad kicked you out... I get to have you all to myself," Marcus whispered, slowly pulling his cock out of his brother, then pushing it back in just as slowly.

Their parents lost their minds when they found out that their precious baby boy had gotten pregnant, though they didn't know their oldest son was the father. They are strictly religious, so they threw the youngest boy out without a second thought, already having barely accepted his 'abnormal' genitalia, expecting Marcus to take care of him.

And boy, did Marcus take care of him.

It was something the older boy laughed at regularly, they apparently figured he would instill some sort of responsibility or discipline in his younger brother or something, but little did they know the two had been secretly fucking since before Marcus moved out in the first place. This pup was the result of them mating during the boys first real heat.

But they both were glad to have a chance to live together.

"F-faster, p-please big brothe-AH!" Jay cried as the older boy began slamming his cock inside of him at a breakneck pace, his paws moving from his brother's hips to his belly and shoulder, bracing him.

"You're so hot like this, Jay... Your pregnant pussy feels so good around my cock, I can't get enough of it!" Marcus moaned as he continued pounding into his brother.

"H-harder! I-I'm getting close, big brothe-AAH!" The 12 year old yelled out, his arms giving out as his body was racked with pleasure.
The older boy didn't slow down, he simply kept pounding away at his little brother's cunt. His own orgasm was nearing as well, but he knew the little boy needed to finish first.

He grabbed the 12 year old's hips again, pulling the boy's body closer to him with every thrust, making his cock go even deeper into his brother's cunt.

Jay couldn't stop himself from screaming.

"YES! YES, KEEP GOING! PLEASE, M-MORE! AHHHH, I'M GONNA-!!"

The 12 year old let out a high pitched squeal as his cunt spasmed around his big brother's cock, his orgasm causing him to see stars.

"SHIT! You feel so fucking good, Jay, fuck, I'm right behind... you...!"

Marcus slammed his hips into his brother one last time before shooting his seed against the closed entrance to the boy's womb, filling him to the brim with his cum, his knot swelling tight inside of his little brother's pussy.

"Ahhh..."

The two dogs lay in relative silence for a while, Marcus still holding onto his brother's hips and the younger dog whimpering happily as his brother's cum filled him up. Canine orgasms last as long as their knots are swollen, so the older dog's cum will keep pouring into his little brother for almost 30 minutes.

Jay shifted and ground down on his brother's knot, trying to milk him for every drop of cum he had, earning a low moan from the older boy.

"Jeez, you're still so eager even after I just filled you..." Marcus mumbled, reaching a paw forward and stroking his brother's cheek, the boy smiling and leaning into the touch.

"Always, big bro. You make me feel so good," the 12 year old replied, turning his head to lick the bigger dog's face.

Marcus smiled and leaned forward, pressing a kiss to his brother's shoulder. "And you make me feel so good too. We were meant for each other, weren't we?"

Jay turned around to meet his brother's eyes, a soft look in the smaller dog's gaze. "We were," he said before he was interrupted by a yawn.

"Well, looks like someone's sleepy. Let's rest up, yeah? I have a few ideas for when we wake up," the older boy grinned, laying down on his side and pulling his little brother close, still connected by his knot.

Jay nodded and cuddled into his brother, sighing in content, drifting off to sleep in his afterglow, cunt still full of his big brother's cock and cum.

"I love you, Marcus."

"I love you too, Jay."

- Three Months Later -

"Full... fucking f-full!"

Jay couldn't move, couldn't think, he could only scream in pleasure as his older brother bred him for the third time that day.

Marcus had his recently turned 13 year old brother bent over the dining room table, fucking into the boy's ass like an animal. His cock was so deep in his little brother, his cum from the first two rounds still dripping out of the boy's cunt.

Jay awoke to light contractions this morning, a sure sign that his labor was near. But his big brother seemed determined to breed the younger dog untill he popped. 

Which, as it turned out, was while his knot was going down from the last time. 

Now Jay's pup was coming, contractions getting stronger and closer, and to distract from the discomfort Marcus was breeding his baby bros ass, and the boy couldn't get enough of it.

"Oh god, I-I'm getting close a-again! You're fucking me so good, big brother!" The 13 year old yelled, feeling a familiar tingling sensation in his crotch.

"Good... how's the baby coming along?" Marcus asked, panting heavily.

"G-good, she's d-definitely getting closer. I-I'm gonna cum again! I'm gonna-" Jay was cut off as his body froze, his orgasm shaking him to the core.

"Yeah, that's right, cum for me. You're gonna be a good boy and give birth to our pup, okay? Then I'll fill your womb back up with my cum, and I'll breed you again, and again, and again. Fuck, I can't wait until you have your next heat. I'm gonna make sure you're carrying another one of my pups as soon as possible, you little bitch," Marcus growled, grabbing his brother's shoulders and slamming his cock in and out of the younger boy's ass all the way to the knot, for a moment the only sounds filling the room being his brother's moans and his hips hitting Jay's.

Marcus could feel the shape of his pup as it descended through Jay's birth canal, the sensation filling him with both anxious anticipation of being able to finally see their baby, as well as a perverse lust, knowing that his cock's movement was helping the birth along.

The 13 year old couldn't form words, he just took everything his big brother gave him. He knew the care that Marcus had for him in reality, but gods didn't the dirty talk turn him even further on. The whole time he had been pushing with the contractions that he could feel, but his brother's constant thrusting seemed to somehow drown out his own bodies sensations.

"Fuck, I can't hold it anymore, I'm gonna cum, you slut, take it all!" Marcus slammed his cock almost all the way inside of his little brother, taking care to not knot him this time, and unloaded into the boy's tailhole.

Jay whimpered as he felt his big brother's cum shoot deep inside of him, the warm feeling helping him relax a bit.

"Ahh, that was good, wasn't it?" Marcus asked, pulling his cock out of his brother, panting hard, trying to recover from the frantic pace with which he was hammering his brother.

"Y-yes, big brother. I love having your cum inside of me, and feeling your cock deep inside of me but... Oh fuck... I think... I think the pup is starting to crown...!" The boy braced himself against the table he was still hunched over, spreading his legs a bit more.

The older dog's ears perked up, and he looked down between his brother's legs, seeing the 13 year old's cunt start to part.

"O-oh fuck, this actually hurts a lot now..." Jay whined, holding onto his belly with one hand and squeezing his brother's paw with the other. Without the pleasure to distract him it was evident how he was probably a bit too small to bear a pup yet, and if not for his brother regularly stretching him out…

"It's okay, Jay, she's right there! Reach down and feel."

The younger boy was hesitant, but reached his paw down anyway. Sure enough, the first bit of his pup's head was there, his vaginal lips begining to spread in a teardrop shape around the mass, and she was close to crowning for sure.

He stroked the sliver of head, feeling the wet fur, in a sudden daze as if it only just set in what was happening.

"I-I'm about to have a baby..."

"That's right, and she'll be here soon. Keep pushing," Marcus encouraged, rubbing the taught, gravid belly that was clenching and relaxing in rhythm.

The 13 year old closed his eyes, focusing on the sensations and breathing deep and heavy. He pushed with every contraction, and could feel the pup slowly moving down. the fingers stroking the crowning pup  absentmindedly moving up slowly, now pressing into his clit, bringing back the delicious, distracting pleasure, enough to build him towards yet another climax and drown out the discomfort of a head larger still than his brother knot stretching him.

"She's so close, little brother, good boy." the older boy whispered.

Jay whimpered, continuing to push and stroking his clit, the sensations becoming overwhelming. "Fuck, Bro... it feels so good... so... b-big..."

"Keep pushing, little bro. You're doing so good. She's almost out," Marcus encouraged.

The 13 year old could hardly hear him, all his senses were focused on the pup coming out of him, the absolute stretch, and the feeling of his clit throbbing in imminent orgasm. His hips rocked gently on impulse, trying to ease the ache in his overstressed pelvis.

"She's coming, I-I can feel it, I'm so close," he whined, stroking his clit faster and harder. "I'm gonna c-cum too... oh I'm gonna... I'm gonna cum the head out!"

Jay gasped, his cunt tightening and spasming as the pup's head pushed out, his fingertips never letting off his clit, now strained to the limit by his vagina gaped wide. He felt a rush of fluids coming out with the head, amniotic fluid and his brother's cum both spilling out of his spasming cunt.

"That's it, Jay, just the shoulders left. Push!" Marcus encouraged, eyes transfixed on what was hapening.

The 13 year old, however, could barely understand his brother, his mind was blank, all his thoughts and senses focused on his little pup and the earth shattering orgasm he was experiencing.

He continued to push, though, if anything on instinct alone, his cunt straining around his baby's shoulders, feeling for a moment like they were stuck. Just as he was about to let off from pushing to catch his breath he felt her suddenly rotate and he felt her come out.

His baby.

Their baby.

"Fuck, she's out. Oh god, she's here, good boy Jay!"

The 13 year old shakily look behind him, and sure enough, his little girl was in his brother's arms, the older boy carefully cutting the umbilical cord. The baby was letting out little cries, her tiny paws reaching out and grabbing at her father's fur.

"Hi, sweetheart. I'm your dad. Your other dad is right here, you wanna see him?"

Jay couldn't form words. his whole body felt numb and tingly, afterglow and endorphins washing his mind nearly blank, and all he could do was reach his arms out towards his little girl. At some point he had been laid down on a bundle of towels, though he wasn't certain when that had been.

Marcus gently passed the baby to his brother, who cradled the little pup to his chest, her cries stopping as she realized she was with her mom.

"Oh, sweetheart, hi... hi..."

Tears ran down the 13 year old's face, he never wanted this moment to end. He held his pup close, nuzzling her nose and cooing softly.

The older dog sat down behind his little brother, hugging him and their newborn pup, kissing the side of the younger boy's face.

"You did such a good job, Jay. You're such a good boy. I love you so much," Marcus whispered.

"I love you too," the boy sniffed.

The new family stayed together like that for a while, Jay's contractions eventually stopping after pushing out the afterbirth, and the baby fell asleep in her mother's arms.

"Hey, Marcus?"

"Yeah, little bro?"

"Do you really mean it? When you say you'll fill my womb back up and b-breed me again?"

The older boy smirked, leaning over to nuzzle his little brother's ear.

"As long as you want it too? Every word."

Jay couldn't help but smile, because he couldn't wait.