>>63643
When you're turning a goody-two-shoes into a big pervert, I find the key is to go for a gradual pushing of boundaries. You start out with easy stuff and then become more and more perverse as time goes on. It's hard to talk specifics with that kind of RP because 90% of the specifics are things you and your partner will decide.
As for physical transformation, the key with that is to think MOLASSES. Slow, sticky, gets all over everything and is hard to get out. Don't just go *pop* you're a succubus now! or *poof* you're a dragon-girl now or whatever the fuck else, transformation is hottest in the details. Describe how the different parts of their body change, or how the gradual changes are affecting how things feel. Try chaining the TF parts together, or having the TF sort of 'spread' across them.
If your corruptive influence is working on their mind (Either through something like hypnosis or directly pouring shit into their brain chemistry), you can play up that angle too. Slip in thoughts that "don't belong" to the character, or- briefly- describe something in a way the character wouldn't in your narration. "She pulled out her fat cock and rubbed it on Kait's face, and it was all the little cat-girl could do to stop herself from… from what? She wouldn't do anything! This was gross! …Wasn't it?" things like that.
Me personally, I like to make my TFs very… sexual in nature, and I like to use the sexuality as the crux, the key point of the character's downfall. Say, a girl who gets turned into a hermaphrodite by this black slime that's pouring all over her body, and the cock is super sensitive and hard, and the goo is pouring in her ears and it just keeps begging for her to touch it, and then when she does touch it she can't stop touching it because it feels so good. And then I can use that, I can kind of tie that to the downfall. So she keeps jerking herself off because she can't stop, or she cums or something and she can feel the pleasure making the corruption go faster. Like every orgasm lets it slip in a little deeper, a little further past her defenses, but it also makes it harder to stop jerking herself off… typically you finish a sequence like that with a 'make or break' sort of moment, one last opportunity for the character to stop.
"She managed to stop her hands… but she was so close! She could feel her orgasm just a stroke away, her balls and her prostate tensed with need. It would be so easy to just… grab it again. But then she'd lose it for real! If she grabbed it now, she wouldn't stop jerking it until the creature had claimed her completely…" Not only is giving your partner a chance to PLAY OUT that struggle usually super engrossing/arousing/what have you, it makes that final release all the sweeter. They're just un-corrupted enough to be aware of what they're doing, but corrupted enough that they can't help but give that last bit up.