Decided to make this a trio of ideas!
Note: For all of these ideas, I want to play the victim. With the exception of Doom, the bad guys/girls can be anyone you desire.Shazam! (transformation, futa, possibly ex or non-con)/b]
For a disclaimer: I know almost nothing about Captain Marvel.
I wish to do an rp based off of this picture: http://pictures.hentai-foundry.com/m/Mlad/69204.jpg
Essentially Captain Marvel does battle with some sort of powerful magical foe (a sorceress, wizard, corrupt love goddess, demon(ess), or so on). After defeating him/her, the villain performs a ritual. The ritual corrupts the magic word (Shazam!) that Captain Marvel uses to change from skinny weak boy into Captain Marvel. The next time he says it, he finds himself transforming into that futa girl..piercings and all. Perhaps some tattoos? Worse of all, he finds that 1.) he can't turn back and 2.) he is actually weaker in this form. He is than beaten down by his enemy and enslaved/broken into being a slave to his conqueror.
You don't have to know anything about Captain Marvel to play this but it might be a good idea to read the wikipedia article at least. The bad guy/girl can also be a character from the comics or an original character.
Gamma Milk! (transformation)Doom Doll
An evil villain (ess) finds out that the milk of She-Hulk would make the ultimate steroid. He/She thinks up a plot to kidnap She-Hulk. Once kidnapped, She-Hulk will be pumped full or hormones and go from powerful muscle woman to flabby, horny green-skinned cow. She will be hooked up to a machine, milked for her gamma milk and perhaps used for pleasure or to breed. In time perhaps she will loose the will to escape as her mind becomes as weak as her body is now.
Transformation/Possible Torments: Huge breasts, huge ass, extreme loss of muscle mass, shaving, branding...anything is up for discussion.
A heroine is captured by Dr. Doom. It can be any female Marvel super-hero or any other open to discussion (Nightcrawler is a favorite of mine). This Dr. Doom can be the normal male one, or even a female version (Lady Doom!). The heroine is dragged before Doom who has a plan. The mighty Doom requires both a play-thing and companion. The heroine will be broken down with a combination of drugs and brainwashing then will be forever sealed away in a suit of feminine metallic armor leaving her a trapped and willing metallic doll/robot, ready to serve her master.Harley Loves Ivy
A different take on the Harley Quinn/Poison Ivy couple. This is a bit loose, so I'll give a basic idea and it can be worked on. I want to play Ivy in either one of these.
1.) Harley Quinn (or Dr. Quinn) falls in love with a patient in Arkham Asylum who is in jail for poisoning their cheating male lover. She proceeds to twist the mental patient into her lover, preying on the poisoner's hatred of men. Eventually she guides her patient lover into creating the persona of Poison Ivy and they proceed to have their love affair.
2.) Same idea only Dr. Quinn falls for a local cop or heroine (Bat Woman?). She proceeds to get the cop/heroine committed in Arkham by trying to drug her/drive her insane. Once in Arkham, she will go about brainwashing her victim into becoming Poison Ivy.Holy Transformation Bat-Man!
Feminization!/Alternate Harley Quinn origin story
The Joker decides he wants a little clown girl of his own to play with. And what better way to get back at the Bat-Man then kidnapping Robin and turning him into his willing play thing? Robin is kidnapped by the Joker and subjected to long torture sessions with the goal of brainwashing, breaking, driving him insane and molding Robin into Harley Quinn.
The Catwoman is tired of Robin taking Batman's attention away from her. So she kidnaps Robin. Why? To make him into her obedient female kitten. Robin will be transformed and feminized than reduced to an obedient little pet kitten to serve at Catwoman's side.