I'm still not good at writing these letters no matter how many times I sign up for these exchanges, but I hope this will be helpful!
So I'll start with general likes and dislikes. I'm pretty easy-going when it comes to fic. The only things I absolutely do not want to read are sexual content (implied sex is okay, just please don't describe it) and major character death. I'm also not a fan of things that stray really far from canon, like mpreg or ABO stuff. So please, none of that. I usually don't mind AU plots though. Other than those things, I'd be happy with anything. I tend to prefer happy or funny plots, and ones that focus on developing friendships, but I'm not opposed to romance or angst either.
I'll try to suggest some plot ideas for each pairing, but feel free to write whatever your heart desires! These are just suggestions if you want some guidance. If you have your own ideas for the pairing, go for it! And feel free to add any supporting characters as necessary.
Please note, the order of everything listed doesn't indicate preference. I'm just writing this in order of how I signed up.
Any of these can be set before, during, or post canon. This is one fandom, however, where I probably wouldn't want to read an AU.
Relationship 1: Hatsuharu and Kyou
I love how hot-tempered these two are. (Well, Haru's only hot-tempered when he's Black) They know how to push each other's buttons and I think that's fun to watch. I think a fic where Kyou gets angry and challenges Haru to something mundane and stupid might be funny. Especially if Haru gets bored and quits halfway through.
Or alternatively, Haru gets the two of them lost somewhere and Kyou has to figure out how to get them back home.
Relationship 2: Hana, Tohru, and Uo
As I said, I love friendship fics, so anything that would explore their friendship dynamic would be nice. Any sort of missing scene of their early years just getting to know each other, or perhaps just a simple story of them hanging out together. Maybe the three of them can have another sleepover party?
Relationship 3: Tohru/Kyou
Any sort of post-canon look at their budding romance would be really sweet. What are the two of them like on a real date? Where would they go? What if Kyou took Tohru on a trip somewhere after they graduate? (Awkwardly late edit: I totally forgot they moved away after graduation, so yeah I'd be happy with something exploring that too)
Relationship 4: Kakeru and Yuki
These two are the definition of a classic comedy duo. Yuki, the no-nonsense one, and Kakeru, the silly clown. If you wrote fic about Kakeru just annoying Yuki (probably by skipping out on student council duties??), I'd laugh so much! The sillier the fic, the better. Like I can imagine Kakeru inviting Yuki over to hang out sometime and Yuki being really disappointed that Kakeru just wants to make ranger costumes for the student council.
Relationship 5: Hatsuharu/Rin
I love these two but there wasn't nearly enough of their relationship in the manga. Literally anything that expands on their relationship (how it started, what happened after the manga ended, etc) would make me happy.
Relationship 6: Kyou and Yuki
This is pretty much a similar dynamic to Kyou and Haru, although they push each other's buttons even more. I'd love to read a situation where they're reluctantly stuck together somewhere, or where they have to work together to avoid something unpleasant. I'm not opposed a fic taking place before the manga begins, but a post-canon fic might be more fun?
Relationship 7: Kyou and Uo
Wow, I'm just now realizing I have a relationship type?? Because again, I love when one character annoys the other. Kyou and Uo didn't get nearly enough time together to just annoy each other. A cute prompt for these two might be Kyou searching for a birthday gift for Tohru, reluctantly asking Uo for help, and chaos ensuing during the process.
Since this show is ongoing, writing something post season five might be difficult, but feel free to write it if you want. I wouldn't mind an AU fic as long as it's not too ridiculous. (Like idk... don't make them inhabitants of Narnia or something)
Relationship 1: Joan & none
An introspective fic about how Joan feels about her life might be interesting to explore. It could be how she feels before she meets Sherlock, or how it is transitioning to detective work, etc etc.
Relationship 2: Marcus/Joan
I'm a shameless Batson shipper. I'd love to read a fic where they finally admit they like each other. Like their friendship naturally just progresses to a romantic one. It's up to you to decide what the catalyst to that would be :D
Relationship 3: Marcus and Sherlock
I actually just like exploring any friendship with Sherlock, especially the difficulties presented by Sherlock's quirks. Outside of their working relationship, are Marcus and Sherlock actually friends? That might be something good to explore.
Relationship 4: Marcus, Sherlock, Joan, and Kitty
I just envision the four of them hanging out one night at the Brownstone, maybe doing something mundane like playing a simple board game. There would be so many relationship dynamics to explore with all of them interacting together.
Relationship 5: Marcus and Joan
As much as I love the idea of them dating, I wouldn't mind a fic exploring their friendship either. They probably bond over how annoying Sherlock can be sometimes.
Relationship 6: Sherlock and none
Basically just the same as what I wrote for "Joan and none." An introspective fic where Sherlock thinks about his life. If you want to go really crazy, you could try to write a fic where Sherlock imagines himself in different life situations (i.e., different AUs) and tries to decide if his perspective on life would have changed or stayed the same.
Relationship 7: Sherlock and Joan
For this friendship, it might be nice to explore what they do outside of cases. What is it like being roommates day to day together? Also, for once it'd be funny to see Joan waking up Sherlock in an frustrating way.
Relationship 8: Joan and Kitty
From one protegee to another. I can see them discussing their mutual experiences over coffee.
Girl Meets World
Another one that I wouldn't mind fics set before, during, or post canon. And again, AUs are fine as long as they're not too ridiculous. Like, a good normal coffeeshop AU would fit these characters just fine. And if you can't tell by my requests, Zay is my favorite character. Somehow. Idk.
Relationship 1: Maya/Riley
I'm still so frustrated this show was on Disney Channel so we never got to explore the possibility of the two liking each other as more than friends. I'd love any sort of fic that would explore how they might finally confess their feelings for one another (preferably not dipping into too much teen angst along the way though). Or I'd be happy with a future fic where they're already together and they just do cute domestic stuff. I'm not picky at all. I just need more girl/girl relationship in fic :D
Relationship 2: Zay and Lucas
These two were supposedly best friends in Texas, but the series never had the opportunity to really show us that. A flashback fic exploring their time in Texas would be nice. Or perhaps, a simple fic of the two reminiscing over home and comparing it to New York.
Relationship 3: Zay, Lucas, Maya, Riley, and Farkle
(Honestly, I wanted to request Smackle too but I accidentally forgot to nominate it. Oops. If you wanna add Smackle in, I wouldn't complain)
It'd be nice to see the group just hanging out together, perhaps trying to figure out a particularly difficult bit of homework. Or maybe going on a short trip together during summer break (to Shawn's house upstate perhaps?)
Alternatively, if you wanted to write an AU: write a story of how the five (or six) of them meet for the first time.
Relationship 4: Zay and Maya
This friendship (possible relationship??) had so much potential and the show wasted it! They'd be so snarky together. I don't care what they're doing in fic together as long as it's fun :D
Possible prompt: imagine them accompanying Riley and Lucas on a date to the movies (during the time when the two were officially dating)
Relationship 5: Maya and Riley
The whole series is based on their friendship, so I wouldn't mind a non-romantic fic either. Anything is fine really
Relationship 6: Riley and Smackle
The show didn't have these two paired up enough when they could have a fun dynamic. Riley is unrealistically optimistic and Smackle is very practical and straightforward. Of course, their worldviews are going to clash every now and then somehow.
Relationship 7: Zay and Farkle
Another wasted potential friendship the show didn't explore. I'd like to see Zay and Farkle try to play that roleplaying game Farkle gave him for Christmas.
NCIS: Los Angeles
Anything set before or during canon is fine. Any mentions of Granger will probably make me cry (but still feel free to mention him if necessary). I don't think I'd really want to read an AU for this fandom, if I'm being honest.
I'm not going to go into each specific pairing for this one because I have no specific requests. I just like exploring any combination of these characters and seeing how they react. I certainly don't mind case fic if you want to write it, but I really would like to see the characters interacting outside of work too. We barely ever get to see that.
Star Trek: Voyager
I'd prefer fics set during their journey through the Delta Quadrant, but post-canon fics are totally fine too if you want to write their transition coming back home. If you want to write an AU, try perhaps just writing a fic set on the holodeck instead? That could be fun in a different way.
Relationship 1: Tom/B'Elanna
My favorite pairing in the history of pairings :D Fic where the two of them are being cute and domestic together would be nice, or also fic where they're angry over something stupid and then make up afterwards. I like all aspects of their relationship.
If you want to write something serious, perhaps a fic where Tom talks to B'Elanna after the episode "Extreme Risk." I always felt B'Elanna's depression was too quickly swept under the rug after that.
Relationship 2: Harry and Tom
Perhaps the two of them playing Captain Proton together would make for a fun fic? I really don't have any prompts for them.
Relationship 3: Harry and B'Elanna
WASTED POTENTIAL! I loved how they nicknamed each other Starfleet and Maquis, and I really wished their different perspectives could have been explored more. They could have been better besties that Harry and Tom, in my opinion.
Relationship 4: Tuvok and none
Tuvok is my secret favorite character. Every time I watch an episode, I'm just waiting for him to say something along the lines of "I'm too old for this sh*t." He doesn't physically look like it, but he's kind of like a father to the crew sometimes. I'd love a fic that would explore that idea.
Relationship 5: The Doctor and Seven
Two characters trying to understand humanity. That's definitely a great point to start exploring their friendship. I also kind of enjoy their student/teacher dynamic, although I feel like Seven should be the teacher sometimes too.
Relationship 6: Seven and B'Elanna
Particularly when Seven first joins the crew and B'Elanna doesn't like her. That's when their relationship was most interesting. A prompt for this pairing can just be two of them being forced to share a table in the crowded mess hall, and perhaps coming to a tiny bit of understanding despite their differences.
Relationship 7: Janeway and Tuvok
They were friends before Voyager, and I certainly wouldn't say no to fic that explored their friendship before they came to Voyager. An additional prompt can just be the two of them sharing advice over a cup of coffee.
Relationship 8: Janeway and B'Elanna
Okay, I really just like watching B'Elanna interact with anyone. I don't even have specific prompts for this. I'm sorry!
So that's it! I hope this has been somewhat helpful. If you need a better idea, feel free to stalk my fics here on AO3 (or stalk my gift fics too for an idea of what I like). Most of my fics are for HSJ fandom but even if you're not familiar with that fandom, they still show the kind of things I like, since I just write what I'd like to read. You can also stalk me over at twitter @Notorious_HAT but I'm afraid I don't tweet about these fandoms very much.
If you're here to write NCISLA fic for me, you can also look at my episode reviews to see how I feel about the show if that might be helpful for you.
Thank you! Good luck writing!