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Marriage is a promise for two people to be together forever. That’s what he learned at first. Tanjirou explained it to him, gently, while Zenitsu chased after Nezuko some more. At the time, he had said: ‘Why would you ever want to be stuck with someone like that?! I don’t need anyone!’ (But he had felt a little strange. He blamed it on the fish bones.)
There are other parts of the promise, too. That was taught to him later, in the shadowy corners of the Red Light District. Prioritizing a person, protecting another person, fighting for another person’s life; those were all things he had already known about. But in the case of Uzui and his wives, that protection was special. They all looked at each other in a way that was special. They looked at each other first, before they looked at anyone else. (In a sign of growth, Inosuke thought to himself: 'I’d like that.' Then he jumped right back into the battle.)
He learned love independently of all of those things, at several different times, and several different places. He learned a whole lot of things. Many of those things were from one specific person, though. The same person who taught him, without realizing, how it feels to have a frantic heartbeat. What it’s like to be so excited to see someone you feel like you’re going to burst. What it’s like to want someone so close you want to crush them to your chest! Just crush them!
Inosuke’s not a person to be shy of those types of feelings toward other people anymore (at least not nearly as much), so as they got stronger and stronger--well, he can be kind too, damn it! And if he wants to be kind to one specific person, if he wants to grab onto and protect one specific person, then that’s his right! He’s the king of the mountain, and Tanjirou knows that, so if he wants to hug his favorite underling that’s what he’s gonna do! If he wants all Tanjirou’s attention, he’ll get it, god damn it!
Such began Inosuke’s long, long lessons on a very specific type of love. And also (unbeknownst to Inosuke) began the pressure cooker of pining Tanjirou was put in. It's okay, he got better.
They were all in separate rooms in the butterfly house, one night. When there was no one sleeping around him, Inosuke felt a strange kind of itching under his skin. It was weird, and bad, and felt...what's the word? Empty. The room felt empty. What he wanted, he guessed, was the presence of someone else. He’d gotten too used to it, which was dumb. He used to sleep alone all the time! What’s the problem, huh, what’s the problem?
Maybe that was the problem. He didn’t think about that. Besides, there was another prickling unease beneath it--the one that made him want to look. To look, just to make sure his stupid underling was okay. Someone so weak might drop dead in the night, after all.
(A while ago he watched someone important die, and dying had never meant that much before. Things die, and become corpses, and get eaten. For most of his life he looked at dead people and didn’t think much of it at all. When he looked at Rengoku’s body, all he wanted was for him to wake up. It’s different now. Dying feels different.)
He snuck into Tanjirou’s room, as quietly as being Inosuke would allow. Tanjirou twitched in his sleep, making odd, pained faces. Inosuke sat by his futon, wondering why the thought of Tanjirou fighting even in his sleep made him ache.
It’s cause Tanjirou needed to laugh, once in a while. That happy look was Inosuke’s favorite thing in the world. He realized that without much fanfare, with a surprisingly quiet, dawning wonder; better than tempura, better than blankets, better than a good fight, the thing he liked the most was when Tanjirou was happy. When Tanjirou fought, he wasn’t happy.
Well, there’s one thing that definitely made Tanjirou happy. The obvious one! Him, of course!
“Wake up,” Inosuke announced. “Wake up, Gonjirou!”
Tanjirou grunted, and moved, and wiped his eyes--after what seemed like forever in Inosuke’s impatient mind, his eyes opened all the way. “Huh? ...Inosuke?”
“I’m going in there!” Inosuke said, lifting the blankets of the futon. He threw his mask off, since that also seemed to make Tanjirou happy. Who knows why.
“What…? Ah--Inosuke--”
Inosuke dove into the futon with him, wrapping his arms around him tightly. He could feel Tanjirou’s heart beating at a bewildered pace, but he didn’t tense up at all. Which was a mark of how much he trusted his boss, of course! Inosuke felt a rush of pride.
Tanjirou was warm, and his clothes were soft, and he had a good smell, and a soft heart, so Inosuke put his face onto his shoulder and looked at Tanjirou from the side.
“You’re too weak!” Inosuke said, way too obviously delighted. “You were upset in your sleep, idiot! I’ll protect you from demons even when they aren’t real, you got it?”
“Inosuke…” Tanjirou’s eyes were still wide, but he could feel his heartbeat getting faster. In the low light, it seemed like his face was getting brighter. Tanjirou did that, sometimes; went all bright red, for no reason at all. Inosuke liked it. He didn't understand why he liked it, but if he liked it, he's definitely right.
“Going to thank me, right? Well, go ahead! I’m your benevolent king, after all!” Inosuke waited for his praise with a huge smile, because obviously he was going to get it. Obviously.
Tanjirou looked down at him, with a strange kind of expression. His face was a little too sweet, even for him. “You’re…” He spoke with a level of wonder and adoration that made even Inosuke squirm. “You’re a really kind person, Inosuke.”
“Yeah!” Inosuke wiggled, completely forgetting they were supposed to be sleeping. “Even kinder than you! Anything you can do, I can do, as always!”
“I...really love you, you know?” Tanjirou said.
…Then he realized what he had said, in that strange, breathy tone, in his half-asleep and lovestruck state--and Inosuke realized, too, except without quite the same connotation behind it.
Inosuke’s movements became wild and frenzied, waving his arms around and shaking his head. “Of course you do! Of course you do! I’m the person you love most in the world, of course! Why wouldn’t I be? I’m the best! I’m the greatest! It’s only natural!” He said all that, but the way he went utterly wild with excitement seemed to say he didn’t already know all about it.
Out of the corner of his eye, he caught a glimpse of Tanjirou’s beet-red face.
“Hey, you, are you sick?!” He yelled, flailing to go squish Tanjirou’s red cheeks. He didn’t realize that you had to, like, pay attention to what temperature they felt like to check for a fever. He was paying more attention to the fact his face felt soft. “I’ll get you medicine, so rely on me!!”
“No, it’s…” Tanjirou covered his face with his hands.
“What?”
“Um...I…”
“What?!?!”
After a while (a while where Tanjirou got progressively more and more flustered), Tanjirou just spluttered: “I-I’ll explain in the morning!”
Inosuke fell asleep pretty well, and he was very contented, although his ear pressed against Tanjirou’s heart picked up the sound of heavy drums all night.
That was the beginning of a long and difficult learning experience. Inosuke learned that being in love was supposed to be a kind of sacred, special thing, not just something that kinda happened. That was fine, and it felt right. Because his second-in-command is a very special person, and he’s a very special person, so it’s fine! It’s totally fine!
Tanjirou took him by the hands and confessed like he was confessing something really hard; Inosuke had to one-up him even when he felt like he was going to faint, so he screamed: “I love you the most!”
Tanjirou looked at him so happily that Inosuke's skin erupted in goosebumps, and then he burst into laughter.
Which brings us to where we’re at now, after a long while. There’s been a lot more things to learn about love in that long while. There’s also a kind of fear that gets stamped down into you when you lose a lot of people while you’re not even looking. Even after Muzan’s ashes become part of the ground, some things stick to your skin like invisible splinters.
(He starts wearing the mask less than he did before. His face and his life are the only gifts he has left from someone he wants to remember. He has to value both.)
He decides he doesn’t want to forget anything. Not one thing. But he’s sixteen years old, and sometimes he feels like he has to clutch onto Tanjirou harder than usual.
“You better like me,” Inosuke says, leaning into Tanjirou’s fingers in his hair. “Cause I’m never letting you go, you idiot!”
Tanjirou just laughs. “As if I’d ever want you to!”
Inosuke doesn’t know his birthday, so after most of the year passes, Tanjirou just presents him with a huge plate of tempura.
“Even if we don’t know for sure, I wanted to celebrate.” His voice is soft and kind, as usual. He pushes the plate farther toward Inosuke. “Since I’m really glad you were born.”
Inosuke chokes on a crumb, and has to hug Tanjirou very tightly for a very long time before he can even remotely handle the kinds of feelings he’s having. No matter how much more mature you get, there’s some things that can only be solved that way, you know.
Tanjirou always just laughs, radiating sunshine. He’s always rendered speechless, a thing only one person can do, and he thinks: ‘You better stay with me forever, dumbass Ponjirou!’
Inosuke thinks. He thinks things more and more, things like, “How can I make him even happier?” “How do I be the best boyfriend ever? Wait, I already am, but how do I be even better?!” and all those other very important questions. Because it’s been a while, but it still holds: Tanjirou’s smile is what he likes best in the world, and if he wants to see it, he’s going to see it!
Inosuke is a very smart boy, and his heart and brain are spinning with love. So he comes up with a very smart master plan, naturally.
“Tanjirou!” He yells.
“Huh? Wait, you said--”
“Get married to me, okay?!”
Tanjirou’s entire face flushes. Inosuke takes that as a sign to continue, because Tanjirou usually does that when Inosuke is winning a lot at love.
“Marry me! You want to stay forever with me, right?! And I want to stay forever with you! So promise!”
Tanjirou splutters, “I-Inosuke. That’s a serious thing to ask--”
“I want to!”
“Inosuke--”
“You’re my favorite, so it’s okay! Marry me!”
Tanjirou takes a deep breath, trying to talk past his embarrassment. “Inosuke. That’s...that’s something you do when you’ve been together for a very long time. And it, um, means a lot of things, you know?”
“Like what?!”
“Like,” Tanjirou struggles, “It means we’re really sure...and want to s-start a family...and uh...well, it’ll mean you’re stuck with me forever, won’t it? And what if someday you don’t want to be? That’s not the kind of decision anyone can make after a year.”
Inosuke just stares at him for a minute, wondering how one human being can be so stupid. Imagine thinking he'd ever change his mind??? “I’m not just anyone! I’m the boss of everyone! And I like you the best in the world, damn it, so what’s the problem?!”
“Maybe when we’re older, alright? You can ask me again then.”
“You idiot,” Zenitsu says, slurping udon noodles obnoxiously loud. “That isn’t how you propose to someone.”
“How would you know?! Not a single person you asked to marry you said yes!”
“And you’re just as bad as me now, aren’t you?”
Inosuke looks down at his bowl, utterly horrified.
“D-don’t make that kind of face, you stupid pig!! What the hell?!” Zenitsu slams his hand down on the table. “Tanjirou’s the only idiot that would say yes to even dating someone like you, anyway! You’re lucky his tastes are so backward!”
“Plenty of people would! Kanajirou is just the one I like the best, so I got him!!”
“Ew!” Zenitsu gags. “Don’t gloat in front of me, you’re disgusting! Tanjirou probably said no because he’d rather marry someone who can say his name right, you know? Or read! Or be romantic! Or be able to do anything other than kill deer with his bare hands!”
Inosuke fell silent. Now, he knows Zenitsu is wrong about things 99% of the time. But there’s something Tanjirou said that’s been bothering him. ‘It means we’re really sure.’ In that case, does Tanjirou saying no mean one of them isn’t sure? It’s definitely not Inosuke. Does that mean it’s Tanjirou? Is Tanjirou not sure about wanting to stay forever with Inosuke?
“Hey,” Zenitsu squirms in his seat, looking a little guilty. “Don’t get seriously upset. Anyone could tell he really loves you, you know? He probably just wants to wait until...”
Inosuke jumps up on the table, making Zenitsu and half the restaurant flinch. “Teach me!”
“Huh?!”
“Yenitsu, give me training on how to be a good husband!”
“What?! Hell no!”
“You’re going to!!!”
“No, I’m not!!”
“Then at least tell me how!!”
“Get off the damn table, you shitty moron!”
Sitting through Zenitsu’s Romance 101 class is boring, confusing, frustrating, and generally terrible. In the spaces between Inosuke throwing things, he does retain most of what he hears. Unfortunately, he doesn't know that the advice is all from the trashiest romance novels that side of the century. Zenitsu doesn’t actually have real-world experience. Even if Inosuke knew where it was all from, he probably still wouldn't know that's not a reliable source.
Inosuke still knows Zenitsu is very stupid, though, so he asks for more opinions. Kanroji just giggles and blushes, and says "W-well, for me, I just like guys that are cool!" and Inosuke is already extremely cool, so he has that down. Uzui tells him "Eh…? You just have to protect and love them with everything you’ve got, you know?" which he also has down. Several old ladies he deemed to be powerful tell him different variations on a few things Zenitsu told him, though. Things about cooking, and being romantic...so maybe Zenitsu has been right a few times.
Which is how Inosuke ends up facing Aoi outside of the kitchen of the butterfly estate.
The butterfly estate is a painful place, sometimes. He can’t go without remembering someone who lived there. It was a special person, though. Someone who had an important kind of love, an important kind of kindness, and taught it to him--so it’s okay to remember her. He wants to. Tanjirou does, too, which is why they stopped there.
Since the fall of Muzan, the estate has become less of a shelter for demon hunters in particular and more a doctor for everyone--and, slowly, it seems to be becoming an orphanage. Kanao just can’t help picking up stray children. Kanao, too, has a special kind of kindness. Kanao will be at the wedding, he decides.
The kids run through the halls behind them.
“And why should I trust you not to burn down the house?” Aoi says, hands on her hips. “Why do you need it, anyway?”
“I’m proving I can be a good husband!” Inosuke shouts. Aoi’s eyes go wide. “Let me use it! Please!”
Aoi shakes her head. “Do you even know how?”
“I know how to make onigiri! Rezuko showed me!”
“You think that’s the kind of cooking that will make you a good husband?”
“Yes!” He shouts it so earnestly and so simply that Aoi deflates, and waves him into the kitchen.
Inosuke spends the next few hours making so much of Tanjirou’s favorite onigiri his arms go numb. Not eating it is quite possibly the hardest mental challenge he’s ever gone through, and him getting through it with only eating about five just proves how good and strong of a husband he’s going to be.
“Sanjurou!” Inosuke yells, kicking open the door to the room. Tanjirou immediately smiles.
“Oh, Inosuke! Where have--”
“Come outside!” He says, and pulls Tanjirou by the arm before he can ask why.
On a table in the garden, below the light of evening and the hanging lanterns, are the onigiri on a table, surrounded by candles. He did his own studying, you know, and he studied hard! To become the best at something, you have to try! And Inosuke Hashibira is now the best at romance!
“Oh! Did you make these, Inosuke?” Tanjirou turns to him, but gets stopped by Inosuke’s finger on his lips. Here is where Zenitsu’s training comes in.
“Shhh, don’t talk.” Inosuke says, desperately trying to remember all the lines he was taught. “Pretty boys like you shouldn’t talk so much.”
Tanjirou stares at him. “What?”
With wide, sparkling, completely innocent eyes, Inosuke goes on: “Since you said you want to be with a bad boy like me, no matter the cost, you’re mine now.”
Tanjirou clenches his jaw very tight, like he’s holding back from laughing. Maybe that’s the point. “What?”
“I might be poor, and I’m from a family that has nothing…”
“I...you were raised by boars, weren’t you?”
“But I want you to be mine. We might not have much, but I’ll take care of you.”
“Oh, Inosuke, did you learn how to read? Those books are pretty easy to grasp for someone who--”
Inosuke breaks him off with a kiss, which apparently is absolutely key to a romantic situation. He isn’t sure how to look deep into someone’s eyes, and it seems like it might be kinda gross and result in permanent eye damage, so he just pulls away and looks at Tanjirou’s eyes like a normal person.
“Will you marry me?” He asks.
A minute of silence passes, and Inosuke hollers: “I did it! I remembered the whole thing! You have to marry me now!”
Tanjirou stares at him. And stares. And stares a bit more. And then he laughs so hard he doubles over, hand over his mouth.
“Huh? Huh, huh, huh?” Inosuke grins. “I did great, didn’t I? I’m really amazing, aren’t I? You’re overwhelmed with joy, aren’t you? Extremely proud someone so great is going to be your husband, aren’t you?!”
“Inosuke,” Tanjirou says through hiccuping laughs. “I said--I said when we’re older!”
“We are older! It’s been like a month! We’re a whole month older! Did you forget?!”
Tanjirou laughs more, and clutches onto his arm for support. Being a support is very husbandly of Inosuke, and he’d like that to not be ignored. “Inosuke,” Tanjirou wheezes, “Did you ask Zenitsu how--”
“Yeah!” Inosuke yells, quickly realizing this might not be going how he had hoped. “And I did everything right! I made you food, and I said all that stupid stuff! So I proved it to you!”
“Proved what?” Tanjirou says, still sounding extremely amused. “I already knew you’re the cutest!”
“I proved I’d be a good husband! So you can be sure! And I am the cutest, don’t forget it, I’m the cutest in the world! But I’m also gonna be the best husband in the world, so you don’t have to worry!”
“I never thought you wouldn’t be! I’m just saying…” Tanjirou leads him over to sit at the table. He frowns, like he’s trying to think of how to word something. “To have something that special...we have to spend a long time earning it, do you understand? To make sure we don’t regret anything at all, and that everyone agrees with our marriage, even the gods--we have to wait a while, right? Until we’re adults. Right now...”
Inosuke blurts out, without really understanding why, “Are you going to say yes to someone else?”
Tanjirou blinks, then shakes his head. “No way! What would ever make you think that?” He takes both of Inosuke’s hands in his, and places them over his heart. “If you’re ever worried, you can just tell me. I’ll tell you everything about how much I love you ‘til you’re sick of it!”
With his face red and mind spinning, Inosuke shouts: “Go ahead! But that’s not it! That’s not what I was worried about at all! I just wanted to make sure you didn’t settle for anything less than the best, you know!”
“Hehe, whatever you say…”
“Don’t make things up in your head, asshole! I wanted you to promise not to go and die, too!”
“Not to go and die…?”
“You’re not allowed! I wanted you to marry me so you aren’t allowed! The demons are all gone, but you’re stupid,” and Inosuke didn’t mean to say this, and didn’t even realize that was why, but now he’s choking back something he can’t quite place. “You’re stupid, so you’re used to thinking it’s alright if you die! I don’t want you to, though! Cause I like your smile the best! I don’t want you to go somewhere I can’t see you, cause I wanna look at you all the time!”
Tanjirou puts his hand up to his cheek. He leans in, and kisses him, so softly and so warmly it makes Inosuke’s head spin even harder.
“I understand,” Tanjirou whispers into his lips, voice heavy with emotion. “I understand your feelings. Thank you.”
“Don’t say it like you’re comforting me or something!” Inosuke pulls away and shouts. His face is still burning. He gets the feeling he’s lost, but somehow he doesn’t feel too bad about it.
Tanjirou pulls him into a hug, and smiles into his shoulder. “Tell you what, Inosuke,” he says, “If you keep asking, I’ll say yes someday.”
Inosuke does ask him again, many times. More for the principle of the thing. When he’s a little bit too overwhelmed with love, it almost becomes habit to blurt it out. He asks at least once every one of their birthdays, because ‘We’re definitely older now!’
At Kanroji and Iguro’s wedding, he accidentally causes a scene by yelling about how if all you need to do is drink from the same cups, what’s the big deal?! Was Tanjirou tricking him this whole time?! They’ve even eaten from the same plate! Their mouths have even touched directly! They’re quadruple married at this point!
It takes a while to explain that to him. Kanroji thinks it’s very cute. Iguro might murder him the next time Inosuke’s there and Kanroji isn’t, which will be another scene entirely.
Inosuke decides it’s fine to wait, as long as Tanjirou isn’t going anywhere. And so, he gets older. He understands more. It doesn’t go away. He still would very much like to.
About five birthdays in, Inosuke announces “Marry me!”
Tanjirou considers it, beams, and says: “Absolutely!”
It takes him about five whole minutes to process it. That five minutes is the only five minutes he isn't talking about it for the next year.