These transformation stories are one of my favorite types, where the main character consensually with a little mental prodding (or none at all) decides to do something they should not and that leads to the transformation of their body and sometimes their mind.
Here’s two that I have returned to several times when I’m in the mood:
http://agrowingconcern.com/personaldemon.html
And two from the site
Do you guys have any similar stories that get you keep coming back?
“The Singlet” is one of the hottest stories on this site.
I have come back to that story a countless amount of times.
[CARNIVAL TRANCE—A MESMERIC JOURNEY IN FIVE PARTS] Skeeter, Craig, and Mike stumble into the world of Master Mezmer, a carnival show mesmerist. The Master turns the young men into sex-crazed sailor-boys and mechanized hypno-units - and finally takes them to an arena in which they engage in a combat of erotic submission. Along the way, first-person narrator Skeeter wrestles with his repressed feelings toward his two sexy friends.