Not going to continue this, but this is where it was heading.

What I'm skipping over: Dean has a slow-burn corruption without the trigger to bring him back to the corrupted mindset on his own. Sara gets a few more scenes to show that the dildo is changing her body, her boobs grow so much she has a wardrobe malfunction, her hair starts changing to lighter hues until she is blonde. Her "Secretary" alter-ego becomes stronger. She starts being able to deepthroat without gagging on her home toy, which she just told Dean about. He decides to test her with the corrupting dildo.

Also thought about adding cheerleaders, that teacher that asked for raise, but not much would happen with them before this scene.

Sara's mouth watered as her eyes stared at the crimson perfection. She knew he was right: she had to show the fruits of her labor. It was becoming easier and easier to slip into her Secretary persona, especially with the way her new clothes perfectly fit her instead of Sara. And so, she stopped resisting.

Secretary opened one more button from her tops, untied her hair, and dropped her soaking panties. The hem of her silk bra poked out over her opulent cleavage, her thighs rubbing together as her juices dripped down her legs. She swallowed and her spit tasted like wine.

She stepped forward and knelt just at the edge of Dean's desk, mouth opening wide, the tongue slithering out to touch the wood. She had her hands behind her back like a good girl and waited for her Master to begin the testing.

[Insert paragraph about evil side of Dean getting off on this.]

He gingerly took the phallus, imagining it pulse in his hands. He turned it over in his hands, fainting indecision, before grabbing it by it's artificial lips and forcing it into the waiting maw with everything he's got.

The dildo was met with little resistance, a small surprised sound from the woman all the feedback he's got until his fingers touched the soft flesh. He held it there, reveling in the feeling of superiority. Feeling that he had her life in his very hands.

Secretary was in heaven. Her usual dildo wasn't tasty, nor pleasant to take in. It was a chore she had to do, a punishment she had to endure. But this? The way it touched her flesh was not comparable to anything except maybe for Master's cock. Heat was spreading through her mouth like she ate something spicy, yet it didn't burn. Just tingle that grew with every moment. She found it easy to keep it in her throat, again unlike her inferior imitation. Her airway was blocked, but her body accepted that fact with no fight what so ever. If Master won't move his hand, she will stay like this, no matter how much she'd want to breathe. That alone was almost enough to make her cum.

The heat was spreading down her gullet and up to her lips. She felt her miniskirt start to ride up her hips, her bra getting tighter and tighter with every moment. Spit began to overflow from her mouth, the liquid oddly red and sticky. Darkness started creeping in at the edge of her vision.

And then he began to move.

It was just like the spanking again. He wasn't stopping for her to take a breath, he simply moved his hand up and down and she had to take what she could get. She felt her spit entering her lungs along with the air, yet it wasn't as uncomfortable as when she did it at home. More over the way the dildo rubbed her flesh felt just like he was fucking her pussy... her pussy while also high on something.

The Secretary began squirting uncontrollably, staining the floorboards with frankly ridiculous amounts of juices. The Dean was grinning towering over her, his hand furiously pumping in and out. He opened his hand. his middle and ring fingers in the metal ring, his whole palm pressing down on the artificial lips on the dildo's base with every down-stroke. It felt so right! So liberating to finally let himself loose! Nothing bad could ever happen! He was in total control!

He sped up and increased the amplitude of his thrusts. Now the dildo almost escaped out of secretary's lips before being roughly shoved back down until he felt some resistance. Slowly, bit by bit that resistance disappeared, until finally! With a loud pop the crimson shaft escaped it's fleshy prison, hovered in the air, then plunged down like a wrath of god. The Secretary parted her lips again, let the smooth surface slide over her tongue, burst into her throat, and go deeper and deeper and deeper and..!

Slam!

He felt the base hit the lips, her whole body acting like a spring to cushion his hand. He didn't let the pressure drop, instead moving his arm in a circular motion, the shaft hitting different angles all around. Finally, after a minute, he felt satisfied and started lifting his hand. His fingers touched the top of the metal ring.

And did not move further.

It felt like the secretary was sucking on the object in her throat. In fact she looked really out of it. Her eyes rolled far up into her skull, her hands that she used to keep on her back dropped limp by her sides, her body twitching in the most spectacular orgasm she ever experienced (yet again). Oh well. Guess he will just have to break the vacuum seal himself. Just gotta get his fingers between the dildo and her lips and!...

He couldn't do it.

He moved the dildo and her head this way and that, yet he couldn't see her pink lips behind the dildo. In fact it was even hard to make out where her face began and where the dildo's base ending. It was like she herself had these big red plump cock sucking lips, holding a ring in, with something cylindrical just behind her cheeks.

It was starting to get to the end of the second minute since she stopped breathing, and Dean began to panic. Her nose so close to his fingers never expelled any air. With nothing to do, he grabbed the ring -the only part that he definitely knew was the dildo- and pulled up with all his might.

The no longer artificial red lips parted, the crimson sword sliding out of it's sheath.

Dean stared. It was the same dildo. Same base made out of the artificial lips biting on a ring, the red shaft of uncertain length and width... And yet Sara's face now had those same lips, and the inside of her mouth was a smooth crimson cylinder with no teeth or tongue, going deep down.

Then the Secretary opened her eyes.

They were dark red instead of her usual brown. She quickly focused on her Master, such lustful, needy look. Inside her mouth, the surface bulged from behind, as her tongue rose up. It slowly got coated/created out of that same crimson material, seeming to slither out far longer than it should've been able. Then it rolled out, it's tip touching the wood, deep red liquid dripping off it.

And somehow with her throat gaping open and her lungs still blocked, she said in perfect English: "Please, Master! Fuck me!"

So... Yeah. I'm done with this one. Feel free to write more if anyone is willing to continue.