You are watching after a daycare center when Safu arrives unexpectedly. She says her mother sent her there because she's been acting out, and wants you to keep an eye on her. You agree. She seems quite innocent. You decide that you can trust her. Over the course of a week, she slowly starts to corrupt the other cubs.  She shows them videos of animals fucking each other. 
You watch as Safu shows a video to a fox boy who stares at it fascinated. As the fox boy watches the video, Safu is groping his crotch. You can see the fox boy's balls drop, and swell into plump, heavy testicles as large as Safu's paw. The fox boy moans and Safu unzips his pants and pulls out his cock, which has grown hard and throbbing. Safu strokes his cock and the fox boy ejaculates, squirting his semen all over his face and chest.
"Now you know what it's like to be an animal."
The fox boy begins to snarl, acting like a feral animal. His cock hangs down between his legs and his tail flicks back and forth. A large sheath wraps around his cock like a feral fox. He howls and pounces on the other cubs and starts humping them. You can't believe your eyes. What has she done?
You try to stop him but he growls and snaps at you. Safu laughs and tells him that if he doesn't let her go, she'll turn him into a real animal. He runs away and you chase after him. You catch up to him and try to pull him off of one of the girls, but he's too strong and his grip is too tight. His fox cock is knotted into her pussy, his cum washing her young womb. Safu grins, and knows that they can breed. Six large breasts begin to grow on the girl's chest. Her nipples are hard and leaking milk. She moans as the fox boy rams his thick cock into her young, virgin pussy.
"What's happening to her?" you ask.
"I made her more animal than human," says Safu. "Her instincts are taking over. She's becoming a mother and breeding bitch.
The girl moans as the fox boy pumps his huge load into her young womb. The cub's belly swells with cum and her nipples leak milk. The fox boy keeps fucking her, ramming his knotted cock deep into her young pussy.
The fox boy's cock grows even bigger as he fills the cub's womb. It looks like he's never going to stop. The girl's belly is now bulging and full. The fox boy's knot shrinks and his cock slips free. As his cum pours out of her pussy, she gives birth! A litter of 6 kits spills from her womb.
You are horrified, but the cubs seem perfectly happy. They crawl up and begin suckling her breasts. They all have fox ears and tails, just like their father. The fox boy smiles and cuddles with his mate.
"You've gone too far," you say.
"No," says Safu. "I've barely started."
Safu's body becomes more curvaceous. She has a big, soft ass, a pair of massive breasts, and a large sheath between her legs. Making you watch, she grabs another cub and hugs them to her soft body. Their face gets lost in her breasts and they begin suckling.
Safu grabs the cub by their tail and drags them to a corner of the room. She lifts her skirt, showing her thick, hard cock. She rubs her cock against the cub's furry hole. The cub tries to resist, but Safu pushes her dick inside the cub's asshole. The cub moans as Safu's cock goes deeper and deeper.
"Stop this," you beg.
Safu looks up and smiles at you with fake innocence. The cub she's fucking begins to squeal as Safu begins to slowly transform and corrupt them while you watch it happen.
"Why are you doing this?"
"Because I'm an animal. All I want is pleasure, and that's why I'm a slut."
You're shocked by Safu's words, but can't help but get a little turned on.
"This is wrong," you say.
"That's the point," she laughs.
The cub Safu is fucking is squealing and writhing. She's transformed the cub into a mouse with four legs, a huge sheath, and a round, pregnant belly. Safu continues to fuck the mouse girl until she finally reaches orgasm. She squirts her cum all over the mouse girl's fur.
The mouse girl's belly swells up even bigger, and her nipples start leaking milk. Her breasts begin to grow larger and larger. Milk leaks from her nipples and drips down onto the floor.
Safu pulls her dick out of the mouse girl's asshole. You see that the girl has two assholes, and her butt is huge. Her pussy is dripping with cum, and her pussy lips are engorged and throbbing.
"You've really changed her," you say.
"Yes," says Safu. "It's time to teach her how to properly fuck."
"What do you mean?"
"Watch."
Safu takes the mouse girl's hands and makes her grab her own ass cheeks. Safu spreads the girl's ass cheeks and shows you her two puckered, pink assholes. The mouse girl's tail is twitching. Safu sticks her cock in the upper asshole, and the mouse girl moans. "The more I fuck her, the more she'll change."
The mouse girl's asshole stretches around Safu's huge, throbbing cock. She's still squealing as Safu begins to pound her. The girl's body is changing. Her breasts have grown so large they hang down almost to her knees.
"I'm gonna cum," moans Safu.
"Cum inside me," says the mouse girl.
"Are you sure?"
"Do it."
"Okay, but we'll both turn into animals."
"That's fine with me."
When Safu cums, you see both Safu's and the mouse girl's eyes turn black and feral. They are becoming huge mice, feral, horny. They begin to squeal and fuck, mating in a frenzy. Safu's huge cock stretches the mouse girl's pussy, and her massive, furry balls slap against the mouse girl's asshole.
The other cubs gather around and watch the feral mice fucking. One of the cubs starts sniffing the mouse girl's pussy. Then she licks it, then starts sucking on her clit. Her face begins to transform into a feral mouse, with black animalistic eyes.
The mouse girl starts squealing and her pussy contracts, squirting milk all over the other cub's face. The mouse girl's nipples are leaking milk everywhere, and the mouse cub is greedily licking up the milk. The other cubs join in and start licking and sucking on the mouse girl's nipples. Their faces transform into feral mice, their eyes black. Their mouths are filled with the milk from the mouse girl's breasts, and their bodies become massive, horny, feral mice. 
Safu's and the mouse girl's eyes are still black and feral, their minds totally lost to the lust. They continue fucking like animals, squealing and squirming. They cum again and again, their feral mouse pussies contracting and squirting milk everywhere.
Every pussy in the room begins to stretch open as they all give birth to horny feral mice. The entire room is filled with massive, horny, squealing feral mice, fucking and breeding.
The whole room is a giant orgy, and the sound is deafening. It's impossible to tell what's going on, and it's impossible to see anything except furry bodies and sex.
The mice's squeals and squeaks mix with the sounds of moaning and sex.
You're terrified, but you can't look away. This is the most intense, erotic thing you've ever seen.
The mice continue to fuck, squealing and squirming, for hours.
Finally, the mice finish, and the orgy ends.
The feral mice have bred and given birth, and the room is full of their squeaking babies.
The room is a mess. Everything is covered in sweat, and there's semen everywhere.
You feel paws on your waist and feel a huge feral mouse pull you into a hug against her massive, furry body and six huge breasts. Her massive sheath fills up the space between your legs. She is bigger than you by a lot, but you can see in her eyes that she is little more than a dumb, horny animal. She rubs her cock and pussy against you, her cock and balls rubbing your crotch, her pussy dripping and wet. She squeezes you tight and kisses you. You struggle to escape, but her paws are too strong. She presses her muzzle against yours and you feel her thick, feral tongue invade your mouth. You can't breathe. Her scent is strong and musky, and her huge tits smother you. You try to fight her off, but her cock is growing harder and thicker, and she is starting to moan. You can feel her throbbing member pushing against your body, trying to penetrate your clothes. You can't escape her strong grip. She kisses you deeply and her tongue explores your mouth. You feel her cock pressing against you, and her huge breasts engulfing you.
She pushes you against a wall and pins you with her body. Her cock is rubbing against your crotch, her heavy breasts smothering you. Her huge, horny feral mouse cock is so hard it feels like it's going to burst. You feel her balls against your crotch.
She grabs the front of your pants and tears them open, revealing your erect cock. You are terrified, but the scent of her arousal is intoxicating. Her furry body is so warm and soft, and her breasts are so huge. You are so turned on.
She wraps her paw around your cock and starts stroking. Her touch is so rough and primal, and her fur is so soft. You can't believe this is happening. She strokes you fast and hard, her huge breasts squishing against your chest. You moan as she strokes you, and you can feel yourself getting close.
You start thrusting your hips and bucking into her grip, and she speeds up her stroking. Your moans are getting louder, and her cock is so hard and wet. It begins to push into your ass, stretching you with surprising comfort and ease. You feel her huge, hot balls against your ass, and her huge, throbbing cock penetrates you. You can't believe it, but it feels amazing.
She starts pumping her cock in and out of your ass, and the feeling is incredible. Your cock is dripping pre-cum, and her cock is so thick and hard. You can't believe this is happening.
Suddenly, her huge balls swell up, and her cock gets even thicker and harder. You feel her shoot a huge load of cum into your ass. You feel it gushing inside you, and her thick, hot cum coats your insides. You cry out and squirt all over her, your orgasm more intense than anything you've ever felt.
Your body is wracked with pleasure, and you feel yourself being drained dry. Her huge breasts smother you, and you pass out.
When you wake up, the massive feral mouse still has her cock buried inside of you. She's still pumping her cum inside of you. Her eyes are wild, and her cock is still as hard as steel. You look down and see that your stomach is swollen and round, and your pants are soaked. You are carrying her child.
You try to get away, but her huge, furry body is too strong. Her cock is still thrusting in and out of your ass. Her breasts are smothering you, and her tongue is in your mouth.
Her paws are holding you down, and her huge, hot balls are pressed against your ass. She has a massive gut, and it's pressing against you so warmly. You can feel it growing, as her feral mice brood grows and gets ready to be born. Still breeding you, she gives birth, each of her daughters looking like smaller versions of her. Feral mice, with six fat tits and huge sheaths.

---

One of the new feral mice scurries out the door to find a new victim. With an animalistic brain, she is barely intelligent, unable to speak in more than squeaks. She squeezes in through the cat door of a neighbor's house, rubbing her breasts and fat gut.
In the neighbor's house, a young girl is playing with her cat. The feral mouse crawls in behind the girl, and rubs her fat gut against her back. The girl can't hear the feral mouse's squeaks, but she can feel her fat, pregnant body, and turns around. She sees the big, feral mouse and tries to shoo her away, but the feral mouse just stares at her, and licks her lips.
The feral mouse grabs the girl's head, and starts to push her muzzle against her mouth. The girl is struggling and screaming, but the feral mouse is too strong. The feral mouse's long, thick tongue invades the girl's mouth, and her huge, heavy breasts smother her.
The girl can't breathe, and the feral mouse is so warm and soft. The feral mouse is still giving birth, and the girl's body is swelling, filling up with her feral mouse babies. The girl can't stop her body from giving in to the feral mouse, and she stops struggling.