transfemme Tim/Caroline Hill AU?
I took this to mean an AU where Tim transitions to female and adopts the name Caroline - sorry if you meant something else, anon! No hard feelings? ♡
1. The rest of the bats are the absolute last people in Caroline's life to know. Not because she has any worry about them being transphobic or not supporting her, but because she knows they'll support her too much and it'll get super old super fast. She's got a headache just thinking about the inevitable competitions over who can drop the phrase "my sister/daughter Caroline" in public the most.
(Spoiler: it's Bruce.)
2. That said, she's always been pretty casual about traditional ideas of gender expression, so she sees no need to be particularly secretive about it, either. Nobody suspects anything when she adds a skirt to her Red Robin costume.
3. Jason is the first bat she tells. Partly because they've been getting closer for a while, but mostly because....okay, it's dumb, she's weirdly embarrassed about it, but. He's always making so many plays on "Tim" (Timbo, Timberly, Timmers) and she needs to know what he'll do with Caroline, okay?
(Answer: so much. She gets called Caribou, Carobit, Carrot, and Carrie in the first ten minutes after telling him.)
(It would've been five minutes, but Jason had to take a few to be honored/secretly super overwhelmed that she trusted him enough to tell him. When she hasn't even told Dick or Bruce yet!!)
(Jason does ask whether Caroline wants him to keep calling her Tim, etc. in front of the other bats, but she says no, she's ready for them to know.)
(Funnily enough, the new range of Caroline-related nicknames don't clue anyone in after all - they're too used to Jason having his fun. It's not until he refers to Red Robin as "she" more than once that anyone's like "wait, what?")
4. Caroline has dedicated a lot of her life to The Mission and The Cover and The Wayne Name, but she's not willing to let this be part of that. There's no PR campaign for this, no focus groups. She legally changes her name, drops a press release announcing her transition, and calls it a day. She has zero interest in defending her choice to be who she is and even less care about "how the public is taking it."
5. Going super public the way she does is actually an amazing confidence booster? Not for how people react (again, she doesn't care), but so much of her life is secrecy that being honest is a weird rush. She wants to ride that rush for as long as possible, so for a long while after her announcement, she goes super feminine. Yes she does get up super early to do elaborate hair/makeup styles, yes she does wear the impractical heels and tiny skirts, yes she does wear the hell out of some jewelry. Eventually she goes back to her old "too lazy to do anything but roll out of bed and pull on what's clean" ways, but it takes a while.
(Jason is really thankful when she goes back to jeans and tees because her dolled up look is super distracting.)
(Only it turns out her simple ponytail is just as bad. He can't win.)