Eric woke the next morning to the sound of Rat's sniffling and wriggling. The creature was squatting on the bed, hovering over Eric's thighs, pointy claws scrabbling at his sheath.
Two things hit Eric immediately, the first was the smell. Rat always exuded a gamey musk, its Rat glands always active in spreading a dusting of pheromones around. This morning was different though, the smell wasn't a dusting, it was a wall of Rat sex. Her glands must have been working overtime to have squirted this volume of musk into the room. Even from two feet away it smelled like his face was stuffed into its rat pussy.
"Eerreeekk!!!" It whined piteously and in frustration still trying to get his cock out of his sheath. The other thing hit him as his eyes focused on the creature. All of Rats sex organs were obscenely swollen and coloured. Rat had always had a plump, slick set of pink Rat shaped labia, ready to plump up even more when they engaged in sex.
Now though, the lips were so ridiculously swollen that they looked ready to burst. Her labia were a mound on top of a mound, sticking out purple, shiny and angry. Eric had a momentary flash wondering if it would look like Rat was trying to hide a package if it wore a panty, before snorting at how ridiculous the creature would look with close. Another whine drew his attention back.
"Errrrrkk.. brreeeed." It begged, eyes bulging and mouth drooling. It his him immediately what was going on. Rat was in heat. Something hit him then, something that cut through the depravity and his rising arousal for a moment.
What would happen if Rat got pregnant? What would even come out? He sat up, pulling away from it, causing the Rat to tumble unceremoniously to the floor, where it twisted, presenting its rear and flicking it's tail out of the way and retching. "Brreeeed Raawwt!". Then reaching back in an uncharacteristically human gesture to part her lips with her paws, showing the slick insides.
Panicking he hopped up and closed on the Chronivac. Activating it and with a few presses Rat froze, calmly curled up, and fell asleep, lightly snoring.
With a moments reprieve he willed his rising cock back into its sheath, giving him time to think.
First things first, he sat down at the Chronivac and did some housekeeping. He pulled up all the data on Rat, something he'd not done since before the fateful two days where she willingly renounced her humanity.
The biometric display for rat confirming what he could already see. Rat was indeed now in heat, fushed through with hormones driving it to breed, and its womb primed to accept his rat batter.
Checking a few other stats he saw that it was now 83% baseline Rat, so much further than they had initially thought and toyed with. He was sure it was only 81% when they had finished. Something was up here, he thought, it wouldn't even take a day long session to finish Rat off at this stage. Its IQ was also pitiful, but it still retained some human faculties for now, partial speech was the obvious one.
Filtering through setting he pulled up the mental faculties list. There he saw the rats deepest desires in plain text and number forms. Filtering for breeding he saw a sharp rise in it at the start of the day he had begun mutating her. Apparently seeing the image of her as a Rat had kicked off the fantasy of becoming a rat brood mother. All the way down her priorities were becoming as ratty as possible, to become as depraved as possible, to breed as much as possible. Those were then, and even now her top 3 priorities. She wanted to be bred. She wanted to be more Rat like. And she wanted to be a depraved animal.
Eric's cock slid from its sheath again, pink and pointy as his balls churned at Rats desires to just be a brooding Rat queen.
Still. This seemed like a watershed moment for the disgusting Rat. It was a shame that it was so animalistic that it couldn't really appreciate this step.
A thought occured then, a devious one, as Eric turned back to the Chronivac and began punching inputs.
----
Several minutes later Rat uncoiled itself from its slumber, and stretched leaving out an "eeeepp".
Smacking her lips the tiny humans eyes opened and looked around in confusion. She looked down at her cold body and recoiled in horror. This was all wrong! Where was her fur!? Where were her wonderful teats. Hands with long pointy nails shot to her face, what happened to her muzzle and paws... Wait... Why wasnt she just thinking like a rat?
She let out a strangled cry of shock. What was going on!?
An "ahem" turned the now human, though still under three foot tall Lisa to look at the sheepishly grinning Eric.
Finding her voice finally she scratched out an, "Eric!? What's..." She looked down again at her naked pink flesh. "Why?!"
Looking at her was a marvel Eric thought. Even though he had the Chronivac that could set anyone to be anything, the new corrupted baseline pull of Lisa's Rat self was so strong, that it bled into his attempt to turn her temporarily back to human.
Her head hair was scraggly, and Rat grey, though that wasn't that surprising. Instead a lot of other small things really added up. Her front teeth were strongly bucked, her nails and toenails still pointy and far tougher looking than a humans, her ears stuck like dishes out from her head, and her bush reached her navel and covered her inner thighs.
"We're at a bit of a crossroads Lisa." He started. That made her scowl and she spat, "Lisa's not my name... I'm just Rat!".
Eric conceded, "yes, sorry. Had just temporarily set everything back to before we even got the chronivac... " He paused, waved at her general state and added, "well... As best as I could imitate anyway."
She softened, but still looked confused, "why though?"
"Like I said, bit of a crossroads, and I kinda need to check this with you." He said
"Check what?!" She puzzled, intrigued.
"I saw your, well... Like desire list and well. Your Rat self has gone into heat so..."
Lisa's eyes bugged out as she looked down at her belly, placing a hand on it. She remembered that morning as her stupid rat self throwing herself at him and the feeling of being in heat. Her face blushes crimson. "Am I!?" She started.
Eric cut her off, "oh! No... Not yet. Well... That's what I wanted to check. I saw your wants and am ready to offer you a deal."
"A deal!?" She asked. "Yeah..." Eric grinned. "I know what Rat you wants, but I need to check with human you just once. I've set all your inhibition and mental tweak settings temporarily to what they were at back before we started, just left all the memories obviously. And I want to be clear here.
If you go any further you'll be too small for me to fuck, and you'll definitely lose what little intelligence you have left."
Lisa sat forward legs crossed, eagerly listening and licking her lips. Eric pulled the waistband of his pants down. His now human penis springing free and peeking over the edge.
"If you want me to lock you like Rat you is right now, come fuck this human cock. I'll scrub every Rat's cum in the world, and you can fuck anything and everything without fear of slipping further. And I'll pull you back to this whenever you want a temporary break.
Lisa's face was impassive, waiting.
"Or" and Eric pulled his pants down further, shocking her by springing a second cock free under the first one, his pointy, angry Rat cock. "...you come here and I pump unscrubbed Rat cum in you, breed you, finish you off forever, never bring you back to this, even temporarily, and drop you in full time with TomTom and whatever brood you make."