Bakugou Mitsuki and Midoriya Inko had been friends since they were little. They were always attached at the hip despite them being a bit of an odd pair. They at one point had decided that they were going to get married, but that plan changed when they both met their husbands and decided to modify their plans to living in the same neighborhood and having kids who could be best friends as well. They were absolutely ecstatic the day they realized they were both pregnant around the same time.
~
About 9 months later a frantic and very pregnant Inko was driving a very vulgar Mitsuki to the hospital after her water broke while they were having tea. Mitsuki was currently swearing at a panicked Masaru to "hurry his ass to the hospital so she could get this fucking baby out".
That day Katsuki Bakugou was born.
~
Around 3 months later a frantic and very not pregnant Mitsuki was driving a hysteric Inko to the hospital after her water broke when they were playing with baby Katsuki. Inko had come over because Mitsuki was upset that Katsuki wouldn't smile like most babies do at his age and would make the baby equivalent of a scowl rather than smile. Instead of getting Katsuki to smile they got a screaming Inko while Izuku decided it was showtime.
After hours of labor, Izuku Midoriya was born and Mitsuki called her husband (Hisashi having left Inko) to bring Katsuki so they could meet.
Mitsuki sobbed when Katsuki grabbed Izuku's finger and smiled.
~
It was months later now and Katsuki was 9 months and little Izuku 6 months. Mitsuki and Inko were overjoyed to see that their boys were best friends like they always wanted. Izuku was honestly the happiest baby Mitsuki had ever met, he smiled like a little bundle of sunshine, while her equally adorable baby preferred small little smirks (unless Izuku was there then he was smiling up a storm).
At this age, both Katsuki and Izuku had started to learn to babble and crawl. Izuku was proving to be a fast learner and seemed to try to learn off of Katsuki. They would sit in their playpen babbling for hours with their parents occasionally coming over to try to get them to say, mama or papa, so color them surprised when neither of their first words was 'mama' or 'papa'.
Mitsuki had been babysitting Izuku for the day when they both started talking. Inko had come over to pick Izuku up and the moment she grabbed Izuku, Katsuki started screaming and crying at the top of his lungs. It honestly scared the hell out of Mitsuki seeing as Katsuki tended to just scream and not cry when he was upset. It must of scared Izuku too because he immediately started tearing up and squirmed in Inko's arms.
"Oh goodness. Izuku why don't you go say bye to Katsuki? He seems a bit upset," Inko set Izuku back in the pen (Mitsuki grabbed a camera), but Katsuki continued to cry. Izuku made the most determined face a baby could make and laid on his stomach and slowly but surely flailed his way about halfway across the pen until Katsuki joined in and crawled over to Izuku as if he'd always been able to crawl, but decided he wouldn't. What a little shit.
Izuku crawled up to the still crying Katsuki and slapped a hand onto his mouth to stop his crying. Izuku's scrunched up and he started babbling hysterically. Katsuki just stared, tears still rolling down his face. After a few minutes of babbling, Izuku let out a giant smile and yelled out "KACCHAN", then leaned forward and kissed Katsuki's cheek. (Or at least it looked like a kiss, he more or less slapped his mouth on Katsuki's face).
Inko and Mitsuki stared in utter shock, Katsuki also stared before smiling happily and babbling too. As if this moment already wasn't too much for their parent's hearts, Katsuki yelled out "IZU!" then hugged a giggling Izuku.
'Mama' and 'Papa' weren't said for another week or two. This interaction was the reason why nobody was surprised that the first time they walked had been together when they waddled to one another and fell down while hugging (completely ignoring their parents who were waiting for them to walk over to them).
~~
Years later and many milestones shared between the two, Mitsuki decided that nothing the two did could surprise her anymore. Until they both came running in, hand in hand (they were always holding hands. It was their thing) and asked Masaru if he could be Zu's dad too because 'Zu doesn't have one and he's willing to share with Zu'. Masaru looked ready to cry. Then Izuku chimed 'I'm gonna let him have my mama too, Kacchan only has a mommy,'. Mitsuki had to laugh at that.
"Alright you two, why don't we go talk to Zu's mama and see if she's okay with that?" Mitsuki proposed.
By the end of the day, both boys had two moms and a dad.
~
Mitsuki was aware that Katsuki took after her a lot. He was nearly a carbon copy of his mother. That was why she wasn't even slightly shocked to see the serious soft spot he had for Izuku. The Midoriya's charm was strong against Bakugous. They were 4 now and Katsuki had gotten his quirk, and apparently, he had been being a brat with it. A fuming Izuku had dragged Katsuki by his ear up to mother, and proclaimed that "Mommy! Kacchan was being a dummy in the park! He kept using his quirk even though he knows he's not supposed too! He even kept saying mean words!"
"Zu! I'm sorry! Let me fucking go!" Mitsuki was going to scold him for his language (which was totally not her fault), but Izuku seemed to have it handled.
"Nuh-uh! You said another bad word! I'm not gonna marry you if you keep saying mean words at me!". He wasn't going to what now?
"Marry?" Mitsuki asked, kneeling down to her boys.
"Yeah! Me and Zu are gonna get married, have babies, and be the number one hero together!" Katsuki cheered.
"You boys know you can't get married just yet, right?" Someone had to break the news to them, but Mitsuki really wished it wasn't her. The look the boys gave her broke her heart. "You have to wait until your older, okay?"
"Well, then what are we gonna fucking do now?" Katsuki pouted.
"Kacchan! Mean word!"
"Sorry, Zu" Katsuki grumbled and crossed his arm.
"Well, most people date before getting married. It's very similar and you'd be boyfriends instead of husbands. You can do that until your big kids"
Izuku and Katuki stared at each other in some silent conversation. Izuku smiled before cheering an 'okay!' and skipping out of the house with Katsuki.
Mitsuki immediately called Inko to tell her about the cute relationship. Neither realized just how dedicated the relationship was going to be.
~~
The day Izuku was diagnosed quirkless was one of the most emotionally exhausting days of Mitsuki's life. Not because they thought Izuku's life was over, but because it hurt to see Izuku and Inko so distraught. He wouldn't leave his room, and it took Katsuki a good 15 minutes for Izuku to even let him into the room. And the moment he did Mitsuki and Inko were both pressed to the door listening in. Every little hiccup Izuku made broke their hearts.
"Kacchan! I can't be a hero with you," Izuku whimpered out.
"What! Why not!" Katsuki yelled.
"The doctor said I don't have a quirk. I can't be a super cool hero like you!" Izuku cried louder.
"That's fucking stupid!" Katsuki yelled, "We can still be heroes!"
"How Kacchan! I can't do anything!" Izuku cried.
"But you're super smart Zu! You're always doing that nerdy thing where you talk really fast! That means you think super speedy! You can help me beat up the villains and I can protect you! You'll be the first quirkless hero" Katsuki declared. Mitsuki was really proud of her son.
Izuku's crying starts to slow to a stop, "okay Kacchan. I believe you," Izuku hiccuped, then mumbled a small, "This fucking sucks,". Mitsuki didn't want to admit that that made her proud, but that made her proud.
"Zu! No bad words," Katsuki growled. What a little hypocrite.
After the noise in the room died down, they walked in seeing both boys curled up together on Izuku's bed.
~
By the time both boys had reached middle school a lot had changed. Katsuki was still as much of a brat as always and Izuku was still playing Kacchan wrangler, but their passions had shifted. They both were dedicated to being heroes, but Izuku was very determined to focus on being a hero for weaker people. He didn't want to be like All Might anymore, he wanted to be someone like Nighteye, Eraserhead, or Nezu. Katsuki didn't want to be like All Might anymore either, he wanted to surpass him with Zu.
The time the boys spent together didn't lessen at all they just changed how their time was spent. Instead of running around playing heroes, they would go to the local dojo and kick the shit out of each other as training. Instead of running in for snacks after playing outside, they'd go out for coffee dates (they only recently realized that to be dating they should probably go on dates). Instead of Izuku reprimanding Katsuki for swearing, Izuku began swearing back until they had a glaring contest (Mitsuki had really rubbed off on them). They also spent a lot of time sitting in the living room curled up together discussing everything from the next video Izuku was gonna post, to debating if Endeavor should be a hero, to just arguing about the best type of chocolate.
What was really jarring though was just how perfect the two were together. Izuku's calmer nature being perfect to keep Katsuki in check, and Katsuki's confidence rubbing off onto Izuku to combat his more anxious nature. They're mannerism quickly rubbed off on each other, Izuku had picked up a knack for creative insults, and Katsuki could be spotted mumbling just as much as Izuku. Even their daily schedules were completely built around one another, Katsuki would drop Izuku off at dance classes, make dinner for both of them with Mitsuki or Inko, Meet Izuku at the dojo to train with him, then spend the night at one of their houses.
So, color her surprised when an angry Katsuki carried a crying and bruised Izuku into the living room and demanded they switch schools. Some kids at school had started picking on Izuku for being quirkless and 'too girly', and when Katsuki had stepped in the started yelling some very awful slurs at the two. Mitsuki, Masaru, and Inko immediately switched them (Inko making sure to give the school a nice lawsuit for ignoring the issue).
~
Even after they switched schools the bullying didn't stop and Izuku proposed 'Operation: Rule the School'. Katsuki had never despised a plan more. It consisted of Katsuki pretending to absolutely hate Izuku and essentially stake a claim as his main tormentor, so the others would lay off. Katsuki agreed albeit reluctantly and would hurl insults at Izuku all-day while also keeping his lackeys in check. He'd then spend at least 30 minutes a day apologizing to Izuku (or getting an earful if he said something particularly bad).
~
Their third year of middle school had been one hell of a ride for the Midoriyas and the Bakugous. Izuku had become a literal celebrity overnight because of an analysis video Hawks had shared over twitter that gained too much attention for the shy boy, Katsuki had somehow managed to increase the size of his explosions and learned to fucking fly (he'd also taken to calling her hag when Izuku wasn't around, but that's not important), and Masaru had walked in on the boys kissing very aggressively, and they now had to leave doors open when they hung out.
Then the sludge villain incident happened and the boys had their first real argument. Katsuki had been upset that Izuku had decided to rush in to help him because he didn't want to see him hurt. He couldn't explain it correctly and ended up lashing out at Izuku. Izuku understood that Katsuki didn't mean it, but he'd also been shot down by All Might, caught by a villain, and watched his boyfriend nearly die to the same villain, so he may have freaked out as well. Izuku stormed off the studio to clear his head and Katsuki spent an hour talking with his mother about what to do. They eventually calmed down and had an hour-long argument filled with explanations, tears, and apologies. This was the first of many arguments, all of them is because one of them unnecessarily risked their life.
This was also the year that Izuku had become All Might's successor. The day Izuku agreed he informed All Might that his family had to know because he was putting them in danger by taking it and he wanted them to have a heads up. All Might agreed and they were then sat in Inko's living room with Masaru, Mitsuki, Inko, and Katsuki trying to explain the situation. Masaru had agreed as long as it was what Izuku wanted, Mitsuki threatened All Might's life if he were to be severely hurt because of it, and Inko had allowed it as long as All Might took care of her son and trained him properly with the quirk BEFORE the entrance exam. Katsuki, on the other hand, dragged Izuku off to another room and lectured him over the risks, and repeatedly made him promise not to overwork himself with the training. They also agreed that they were gonna keep their relationship a secret from All Might and UA when they got there until they were sure they could trust them.
Over the next nine months, Izuku bulked up by cleaning the beach and sparring Katsuki. Another important event that year had been when Izuku had started training one for all and sent Katsuki hurling into a wall with a superpowered kick.
But of all the achievements that happened over that year, the most important was in two parts. The day they got their acceptance letters from UA, Katsuki had cornered all 3 parents and asked if he could propose to Izuku. He promised that they wouldn't get married until after high school, but "He was so in love with his nerd he couldn't handle the concept of not being with him,". All 3 parents couldn't help but cry and agree. Inko made him promise to take care of her baby, and Katsuki couldn't help, but tear up as well. The adults had all helped plan the proposal and Masaru had taken Katsuki ring shopping while Izuku had a day out with his moms.
The second half had been the night directly before their first day at UA. Katsuki had asked Izuku on their first formal date and they got all dressed up and went out for dinner together. They were for hours laughing and chatting like usual, but what wasn't usual was how much Katsuki was fiddling with his jacket. Izuku kept giving him curious looks until they finished dinner and Katsuki whisked him off to the park they used to play at.
Katsuki had set up a bunch of lights, flowers, and a radio in the middle of the park and asked Izuku to dance with him. They danced for a while, then Katsuki took a deep breath and turned off the radio.
"Izuku. Oh fuck, this is hard. Um, I know this is gonna seem really early, but we've been dating since we were 4, and I just love you a lot, and never want to lose you. I promised our parents that we wouldn't until after high school, but we are so close to our childhood dreams and those dreams will never be complete without you, so," Katsuki got down on one knee and Izuku felt his heart stop, "Izuku Midoriya, will you fucking marry me?"
Izuku lunged at him, practically slamming their mouths together. Both boys were crying and Izuku could barely speak, so he settled for rapidly nodding and sticking his hand out. An hour later both boys walked into Inko's living room, faces covered in dried tears. Izuku stuck his hand up, showing off his ring, he smiled at Mitsuki and yelled, "Mommy! Katsuki said a mean word in the park! He asked me to 'fucking marry' him".
"Oh? I thought you couldn't marry him if he kept saying mean words at you," Inko chimed in.
"Okay. That might of been a bit of lie," Izuku chuckled and smiled at Katsuki.
Katsuki grabbed Izuku's hand and smiled.
~~~~
After all the heartfelt moments Mitsuki had witnessed through her boys' lives she never once thought she'd end up where she is now. She's currently looking at a picture Izuku had sent her. It was of Katsuki glaring at a board labeled "Find ZeroTheHero" (the words 'conspiracy board crossed out), in the opposite corner of Katsuki was Izuku's hand, engagement ring very prominent, gesturing to a small post-it note on the side that said: "Bakugou too mean- Definitely not dating Izuku". Mitsuki promptly lost her shit.