trans boy!deku
Katsuki and him still have a rocky relationship but it’s never based on Izuku’s gender (I headcanon that Katsuki really doesn’t give a flip about what parts you got under your belt, so long as you’re strong, he’ll respect you). In fact, Katsuki would be the first person to defend Izuku if someone misgenders him (”YOU CAN CALL HIM A WEAK, QUIRKLESS DEKU BUT HE AIN’T NO GIRL YOU ASSWIPE”)
Featuring utterlySupportive!Inko, notATotalDouche!GenderNormBlind!KindOfOverprotectiveBrother!Katsuki, generallyHelpfulIfABitBadAtExpressingHimself!dad!Might l (which is kind of normal now that i think of it), and pretty much really cool class 1A (even INeedToRethinkMyPrioritiesDoILikeWomenOrCurves!Mineta)
Shipping optional but always fun. Probably not KatsuIzu in my mind, but anyone else is pretty epic.
Additional info below;
Like I said, Katsuki is kind of like Izuku’s really awful, overprotective older brother (”But Kacchan! You’re only like… a month and a half older than I am!” “Shut it Deku, as if I’ll let that half and half bastard take you out for prom” yes i know, japan doesn’t normallg do prom shutup, it's an example). And because he doesn’t give a flying flip about gender norms, he’s totally the guy who’d say “Pussy up” or call someone a pussy as a compliment (like, hello, that thing pushes out a fucking baby, pussies are awesome, take it as a compliment ass!).
Imagine, the first day at U.A. – there’s a mixup with the uniform that Izuku is sent because his records still has him listed as female so U.A. sends him a female uniform (because Japanese laws on LGBT rights are still really iffy and you can only if you get an SRS and if Izuku is, yanno, saving to get everything done in one swoop, even with his mother’s support. If Hisashi isn’t around or is actively against it, then he might not even be able to get reassignment surgery until he hits legal age @ 20 which further complicates matters). And Izuku is upset because, fuck, his dream is already being blasted but he’s like.. “I’ll just go in today with the skirt, bring the extra ones with me and get them exchanged for pants at the school store in the office”. One day. He can totally deal with one day in a skirt, right?
And while uncomfortable, Izuku perseveres because it’s fucking Izuku, but then he gets there and the store’s not open yet and won’t be until, at the earliest, later that day (or even later that week – it’s not unusual for stuff like that not to be active until class reps and everything gets voted on) so he begrudgingly and awkwardly makes his way to Class 1A.
He still meets Uraraka at the door, and she’s surprised because, wow, she thought he was a boy during the test, sorry for calling you that ahahaha (but no, Izuku was really flattered, even though Uraraka called him the plain looking boy with curly hair when talking to Present Mic), and Katsuki still blows up about seeing quirkless little Deku in his class again.
Except the blow up is less “how did a quirkless loser like you make it here!?” and more “what the fuck are you wearing, you fucking hate skirts, you idiot!” And Katsuki is revving up to pull Izuku to the nearest bathroom and yelling about if he’s going to be stupid and uncomfortable, how about he be stupid and uncomfortable in his pants (because yes, Katsuki is a jerk, but he’s secure enough in his masculinity to wear a skirt especially since he knows he’s got the legs to rock it, and he knows just how much Izuku hates looking like a girl).
Of course, Aizawa-sensei stops them; instead of going to the start of the year assembly for his aptitude test.
Katsuki still pulls him to the male changing room and the moment someone (Probably Mineta, maybe Kaminari) says something, he’s about to scream something back but Izuku beats him to it. He clearly states “I’m a guy” (maybe even tossing in a “yeah I’m not built like you, but get over yourselves unless you’re trying to overcompensate for something”) and gets changed into the gym uniform.
(of course, Kirishima is like “wow, that’s manly”)
(later on, maybe at the end of the day, Bakugou gives Mineta a piece of his mind because holy shit, he’s a creep, and lets him know that if Mineta pervs on Izuku, he’s going to say he's not actually a ladies man when he bats for the other team)
Also! All Might doesn’t know Izuku is a trans boy until maybe… two or three months into Izuku’s training. Izuku has ridiculously bad cramps, so he misses school, but he doesn’t want to miss cleaning up the beach but he honestly can’t move because fuck you cramps.
And then All Might calls but Izuku’s phone is far away, so Inko picks it up, and All Might starts talking about how surprise he is that Izuku isn’t early for training as he usually is, and is there a problem and stuff like that.
And then Inko goes off on this unknown man, who’s suddenly “training her child” and don’t you need permission and she swears to all the kami that if he’s a pervert trying to take advantage of Izuku’s good nature and the fact that he’s not built like other boys, there will be hell to pay, leave my boy alone you pervert, he’s on his period, etc
Now, All Might’s floundering like… he didn’t know Izuku would have to deal with periods?? He didn’t take into considering that because he honestly didn’t know so eventually, after Inko takes a breath to keep going he’s like “Ma’am, your son is a fine, outstanding young man and I did not know that I would have to take into account a more painful than normal menstrual cycle when I drafted up my training regime. Please give Midoriya-shounen my regards and some hot water, and tell him to take it easy for the next few days, and I’ll see him when he feels capable of moving”
And that, that right there, makes Inko and this “Yagi Toshinori-san” hit it off
(imagine, Inko and Toshinori start dating a little while later, and Izuku is mortified because “holy shit, my mom is going out with All Might but I don’t know if she knows he’s All Might, what do i say!!”)