You are awesome! Thank you for writing for me! I hope you'll enjoy writing your story as much as I'll enjoy reading it!
I love all of these fandoms and all of these characters and will love fic about any of them, so if you already have an idea, then go for it; I know it will be as rad as you are! If a little detail from me will make things easier/more fun for you, then I'll ramble about fic in general and these particular fandoms/characters below:
Do-Not-Wants: I'm fortunate not to have any triggers, but I do have a couple of back-button squicks that it would be great if you could avoid: romanticized/eroticized depictions of incest or rape are deal-breakers for me. If canon and/or the direction your story takes you include incest or rape, I'd prefer it not be depicted in great length or graphic detail. I'd prefer no a/b/o or mpreg. If you're moved to porn, I'd prefer nothing that kinks on fear, extreme pain, or risk of death or maiming.
Stuff I love, in general: banter, found families, redemption narratives, missing scenes and tags/codas, gallows humor, h/c that's light on the 'hurt' and heavy on the 'comfort', characters playing poker, women kicking literal and/or metaphorical ass, characters who own their mistakes (even if they can't seem to quit making them), double lives/secret identities, and hopeful, if imperfectly happy, endings. Most of my favorite stories could be distilled down to something like broken people make a home for each other and/or ragtag band of misfits save world, one another.
[Other General Details] Shipping News: I love gen fic a lot, but I'm also open to stories that include m/f, f/f, m/m, and poly relationships. I especially like UST, casual sex between characters who have respect and fondness for each other, and established relationships. Generally, I don't have a lot of unshakeable SRS BZNS shipping preferences (so feel free to sell me on any relationship that doesn't rely on abuse of power), but I'll try to give you an idea of any ships I have strong feelings about in the fandom-specific sections below.
Stylistically: I don't have a dog in the past tense vs. present tense fight; I read, write, and enjoy both. I will always be a sucker for any kind of unusual narration: second-person, 1st-person plural, outsider POV, unreliable narrator, epistolary fiction, omniscient narrator, etc., etc., ad infinitum. But, third-person-limited is popular for a reason -and that reason is that it works!- so please don't feel pressured to try something you wouldn't have fun with. Just know that if you were thinking about experimenting, you'd find a receptive audience in me!
FANDOMS! ♥ My fandoms are listed below alphabetically, and if the herds of tl;dr associated with each one come in at different sizes, please know that's a function of how many characters I've requested and not a reflection of different levels of enthusiasm. I love all of these fandoms to a truly ridiculous degree, and will be delighted with wherever you end up writing for me!
I was unprepared for how much I would love Sam Wilson! I love his steadiness and empathy and kindness, and I love that he is an action hero who is also skilled at and finds value in taking care of people emotionally, and I will love any story you care to tell me about him! I'd love to read about his past, particularly his time in the service and the path that takes him to the VA position he holds as the movie opens. What was going on in Sam's life when Cap was discovered and revived? How did that news (or other superheroes-are-real/MCU-event related news) affect him as a non-enhanced soldier or civilian? How will he balance that life with increasingly frequent acts of non-powered heroism?
I love (or at least really like!) pretty much everybody else in the MCU, so feel free to include any/as many other characters as you like. Below, I'll throw out a few general ideas:
Sam and Steve crossing things off of Steve's list of things he missed. Sam and Rhodey bond over flying and working hard to keep friends out of trouble. Other times Sam's offered Natasha a safe place in trying times. There are only a few people Maria Hill truly lets loose with; Sam Wilson is one of them. Sam meets Peggy Carter on one of her better days; they talk about lots of things, but especially Steve. Sam is invited to [Avenger/Supporting Character of your choice]'s regular-ish (potentially-world-ending-crises permitting!) poker game.
I'd also love to see missing scenes from the movie, like: more of the time when Steve and Natasha crash/hide out at Sam's place; the heist to recover the Falcon gear; bedside vigil time at the hospital with Steve; or anything else you wish they'd shown us.
I'm currently fairly un-spoiled for Age of Ultron, so I have no specific prompts to tie into it, but I will almost certainly have seen it before reveals, so feel free to incorporate any character beats or fallout from its events.
I've received lovely gift-fic about Sam previously, but rest assured, I'll always be delighted to read more of him!
Shipping News: I would eat all the gen friendship fic up with a spoon, and I have a bit of a soft spot for Sam/Natasha/Steve, but I'm generally happy to read Sam shipped with anyone who appreciates him. If you put Sam at the center of an ensemble story, I'm cool with pretty much any background relationships except Thor/Loki or other incest pairings.
I will be delighted with any story you care to tell me about Maya Hansen before, during, or after the events of Iron Man 3! I just really love her arc through the film, from her early idealism, through a series of compromises that eventually leave her complicit in "The Mandarin"'s atrocities, to a final effort at resistance even though she must have expected to wind up gut-shot and deserted for her trouble.
I'd love to hear about her early career: the conception/initial development of Extremis and the course that brought her to the conference where she connected with Tony and Killian.
The Extremis trials are pretty endlessly fascinating to me, so I'd love to see Maya during them, weighing the project's progress against against its steadily-increasing human costs, and drifting away from her initial purpose so gradually she doesn't even notice at first.
I'd also adore a Maya!Lives story set after the movie, in which she gets a chance at a redemption arc, whether that comes in the form of working with SHIELD/refusing (or betraying?) HYDRA or any other direction you see fit to take her.
I'm currently fairly un-spoiled for Age of Ultron, so I have no specific prompts to tie into it, but I will almost certainly have seen it before reveals, so feel free to incorporate any character beats or fallout from its events.
I've received wonderful fic about Maya in previous exchanges, but if fandom worked according to my whims, roughly half of the MCU fic in existence would be about her.
Shipping News: I would be perfectly delighted with gen, but if you're inclined to write something shippy or porny, bring on all the Maya/Pepper and/or Maya/Pepper/Tony, please!
I'm familiar with major plot beats and differences in tone across the various adaptations and iterations of the Turtles' story, so please feel free to work from any version you prefer or are most comfortable with. (Though, if you use April as a point-of-view character, I would generally prefer that she be a bemused adult rather than a teenager.) I don't want to prompt too specifically and box you out of the version of canon of your choice, so I'll mostly ramble below about things I love about the fandom, in general.
The Turtles' story is one I will always come back to happily, like the narrative equivalent of comfort food. I was exactly the right age to imprint hard on the original cartoon series and first live-action movies, and I can see echoes of TMNT in a lot of the kinds of things I'm drawn to in a story, even now: families - especially families of choice, ridiculous action pieces/fight scenes, a universe that posits interesting, and sometimes dangerous, secret worlds just under the surface of ordinary life, heroes who are never fully a part of or at peace in the mundane world they risk themselves to protect; Raphael was always my favorite as a kid, and to this day I remain a sucker for characters who are sarcastic and stubborn and less hard than they'd like you to believe.
Before little!me had any inkling of something like fandom or fic, my many and sundry action figures would often be found acting out melodramatic - because mutants can't just go to the doctor! and what will they do if Master Splinter or one of their brothers doesn't get better?! - hurt/comfort epics. I like to think my tastes are slightly more subtle these days - running less to comas and open weeping and more toward distressing but not permanently debilitating injuries and snark and affectionate abuse that utterly fail to disguise fear and relief and other squidgy emotions - but there aren't many things I dig as reliably as hurt/comfort.
With a group of four characters, we get all the individual relationships (Donny and Mikey, Mikey and Raph, Raph and Leo, Leo and Don, etc), plus the ways all those dynamics interact when any three or four of them are together. I love them all, and I love stories about siblings, so a story about any combination of Turtles just being brothers - whether goofing off over pizza in the lair or in the middle of a more fraught situation on the surface - would be awesome! Likewise, fic about Master Splinter and fatherhood would be lovely.
I also really love lightly fluffy gen de-aging fic in fandoms with sci-fi or magical elements, and if that's something you're up for, I would definitely eat that up with a spoon here. I have no real preferences as to who should end up regressed and who should be left to caretake/puzzle out a solution, as every possibility is a delightful one: (Casey turns out to be surprisingly good with small children/turtles; Leo is suddenly little and has to let everyone else be responsible for him for a change; who knew Master Splinter was such a picky eater?, etc.)!
Shipping News: I'm going to be no fun at all here, and say that I'm only interested in gen fic out of this fandom. I'm not comfortable receiving any porn for this fandom.
One fandom-specific Do-Not-Want here: I'd prefer your fic not use the performers' real-life names or any details of their personal lives and relationships that have not already been incorporated into kayfabe.
IIRC, in order to match with me on this fandom, you'd have to have offered all three of these characters, but I'd be perfectly happy with a story about any of them individually or any pair of them one-on-one if that's what you're feeling.
One of my favorite things about this fandom is the intimacy/frustration of constant travel and living in each others' pockets, so I'd be delighted with a slice-of-life-on-the-road during their run as The Shield, or something set after Seth's heel turn about how weird/hard it is for Roman and Dean to reshape their routines around his absence and/or how Seth adjusts to traveling alone or with various members of The Authority.
Feel free to stick close to kayfabe storylines or take up a divergent AU: I'm especially partial to Seth's-betrayal-is-a-long-con-on-the-Authority scenarios and futurefic wherein the Shield has reunited but not necessarily gotten past all their heel-turn related baggage. In general, I am utterly here for any and every kind of angst about Dean's abandonment issues, Seth's heel turn, Roman's travails from the Rumble onward, but I'll also throw out some tropey and/or fluffy prompts below:
Roman is distinctly unenthused about doing press for the Immortals video game in his character's centurion costume, leather battle-skirt and all... until he sees the effect it has on his partner(s). I leave to your discretion whether that's as fluffy as giving them something to laugh about on a tough day or as smutty as frottage ensuing when they can't break apart for long enough to disrobe or anywhere in between. Mostly, I'd like to see Roman enjoying taking care of someone(s) he loves, in whatever form that takes.
If I had my fannish way, the curbstomp-onto-cinderblocks would have spawned reams and reams and reams of tropey, soap-opera amnesia fic about Dean: where was he during the month or so he was missing from programming? what would he do with the shreds he does remember? what happens when others encounter him and figure out what's happened - who'd try to take care of him? who'd manipulate him for their own purposes? Seriously, go nuts here.
I have a lot of feelings about Seth and the Authority, especially J&J Security, who are unfailingly loyal to and inexplicably fond of him, even at his weaselly worst. The Authority are definitely not the Shield, but sometimes they're almost a (dysfunctional as all hell!) family, too. What's it costing him to be part of it? Anyone can see the benefits of power; are there less-obvious perks to having bought-in?
Shipping News: Found-family gen is always a delight, and Dean/Roman reliably turns my heart into ridiculous mush, but I also ship every possible combination of these three; there are no wrong choices here, only excellent options.
I hope something in the above tl;dr is helpful to you. If not, please ignore it; my intent is to give you options, not to box you in. Thanks again for writing for me! I hope you're having a great fest! ♥