Ideas for male to futa transformation?

Story by nihao2u

I enjoy working at story concepts in my spare time, even though it rarely develops beyond a few initial scenes and isn't worthy of sharing. Lately I've been trying to think of a story concept involving a male main character turning into a futanari, and come up empty, at least for a concept that just intuitively 'works'. So I was hoping other people might have some suggestions.

To be precise, I'm thinking about the kind of futanari that is most popular on this site: beautiful and feminine, but very well-endowed and generally the dominant or at least taking on the traditional male role in sex. The Internet is full of stories about men becoming 'shemales', but this is largely limited to sissification/emasculation stuff where the guy experiences penis shrinkage or even castration/complete gender reversal, and becomes essentially a submissive woman in bed. There are of course stories about 'dominant t-girls' rocking some dude's world, but these are pretty much always from the dude's PoV and the existence of a really hung, dominant tgirl isn't really justified.

There's also a few male to futa stories around, but they generally involve it being the desire of the male. I generally prefer unwilling transformation stories however, where the hero is 'stuck with it' as opposed to being a unashamed pervert from the start (must be residual shame from my Christian upbringing... :)))

I can see why it generally makes sense that a woman growing a penis is empowering while a man getting female secondary sexual characteristics is dis-empowering... and also, a woman getting a penis is '1 thing', a man becoming a woman AND getting a penis is '2 things' (since a man becoming a woman would normally diminish or remove his penis, as estrogen treatment does in real life). So, for example, to me, it seems to 'makes sense' if an errant wish, a newly revealed supernatural heritage, a 'genetic nanovirus', some nebulous conspiracy or whatever other common trope causes a girl to become a futa. Or a man to become a woman. But not for a man to become a futa.

I prefer stories that make intuitive and elegant sense and require as few implausible things as possible. It is better if HalfVampireAmy who believes she's human discovers the secret world of vampires because a werewolf smells her ancestry and attacks her, starting her quest. Than if HalfVampireAmy just coincidentally happens to be at the graveyard when two vampires start fighting, one of whom just happens to be her father, and the vampire king, or whatever. Oh, and her best friend from childhood also discovers she's a witch.

The only 'loophole' I've found so far is a setting where there's a contrivance that turns men into the ideal woman of someone, and by chance the protagonist is turned into a futa because that's someone's ideal. But I don't like that setting much.

Sorry about the long ramble. Let me know if it's just me overthinking things really hard, or if you have any ideas.