this may one day be a fic. but probably not so here
so for the sake of this working we assume yachi went to university in osaka, still doing like, marketing & design
and one evening she's just walking home tired from class and decides to buy takeout rather than cooking by herself. it's spontaneous so she just walks into the next building that says "onigiri" on it without thinking about it much
instantly starts panicking when she sees it's basically empty tho like is this even a restaurant? is there real food to be bought here? is this a yakuza front? is she about to get murdered for daring to step in here?
except obviously it's not, and she gets greeted by a cheery "hi what can I get fer ya?". but she startles and squeaks, and then when she hears "oh, aren't ya the girl who" she just panics, hits a chair trying to go backwards and falls over, then scrambles and runs right out of the restaurant.
now osamu is pretty clueless as to what exactly just happened, just that a girl walked into his restaurant, he recognized her maybe as the girl who was karasuno's manager and that he almost hit with his serve like three years ago, and then she screamed and ran back out. and also dropped the wallet she was holding.
and because he's a reasonable person, he doesn't pick up the wallet and waits to see if she comes back, no, he takes it and books it after her
it's not even really night yet and they're in a big city, so they definitely get a lot of stares, and when osamu catches up to her and grabs her arm to stop her from running again he has to very loudly go "you forgot your wallet at my store! you should take it with you before you go!" because multiple passersby have their phones raised to call the cops on him. like sure he's just barely still a teenager at this point and only a year older than yachi, but he's WAY taller and yachi looks younger than she is and also she's probably crying just from the shock
poor girl is so embarrassed by the scene, takes her wallet back and bows like five times in apology for troubling him like this and only then looks up enough to see that oh. she does know who this is
well. as she puts it "oh, you're miya - uh" looks to his hair. not dyed anymore. looks to his chest. no numbered jersey (why would he be wearing that now?). "um. one of them." then immediately apologizes because that's so rude, she really should be able to tell them apart
osamu just laughs it off, gives her his name and introduces himself as the one who used to dye his hair grey and didn't play setter
also admits that he has no idea what she's called either, so they're even
yachi introduces herself and feels a bit more at ease, enough to agree to go back to the restaurant and buy some onigiri which was the original plan anyway
osamu offers to give them to her for free as an apology for spooking her, but she insists on paying, so osamu just hands her some extra ones that are left over that he probably won't sell anyway
yachi leaves with her onigiri, now way too much for her to eat, and shares them with her roommate
both of them are blown away by how good the onigiri are and the roommate is like. idc how much you embarrassed yourself we are gonna go back there. regularly. this is not up for debate.
and like. yeah. those onigiri are worth it. and osamu didn't seem upset or like he was making fun of her either. though she's still 100% sure she completely blew her first real impression on him.
meanwhile osamu's just hoping she likes his onigiri, thinking she's cute and funny
next time yachi goes to get food by herself she actually sits down to eat, and osamu chats with her a little. just casual stuff, what yachi is doing in osaka, kageyama is on the adlers now so he'll play atsumu next week since he's on the jackals, also he wants to know what hinata is doing rn, what do you mean he's playing beach volleyball and learning portuguese to go to brazil?
pretty soon it becomes easy for yachi to come and it's her go to place for comfort food, and she sometimes brings her new uni friends as well
it slowly spreads as a secret tip among the uni students but it's still empty a lot of the time
yachi starts wondering if maybe she isn't the only one not quite sure if this is actually a restaurant and people don't come in since it doesn't really clearly say anything outside
it's on her mind so when she gets an assignment to design a business logo and some ads she does it for onigiri miya
shyly presents them to osamu later and he's like "wow this looks so good you're incredible"
and yachi is blushing cuz he's really close to her looking at it and why is her heart racing like that? she offers him he can use it if he likes, which he refuses because he can't really pay her, but she says she's already made it and got a good grade so. it's not like she did this for money or will get paid if he doesn't use it.
so she helps him get the logo printed for the storefront, and he makes flyers out of her ads, and she draws on a chalkboard he sets up outside.
it ends up helping a bunch more people discovering onigiri miya and boosting business, she also makes him a website later, for another assignment.
and they get really comfortable, just hanging out. yachi doesn't even startle anymore when atsumu randomly barges into onigiri miya cuz she gets used to him. surprisingly she finds the twins bickering soothing. it reminds her of kageyama and hinata. osamu gets drawn into yachi's friend group, so he's not just working or hanging out with atsumu's friends on the jackals all the time anymore. yachi becomes onigiri miyas second taste tester after atsumu has confirmed it's edible.
and somehow, osamu is still surprised when atsumu eventually asks "so when are ya gonna ask her out, huh?"
as if he's not talking about how cute yachi is all the damn time, or how hard she works or how talented she is or how his restaurant seemed quiet and wrong those two weeks she went back to miyagi to visit her family.
it has been suggested to yachi by her friends and roommate as well that osamu might be into her but uh. she has immediately catastrophized all the ways her doing anything about this possibility could end in her social ruin so she has tried not to entertain it. her mother always lecturing her to be careful around men and their ulterior motives and general uselessness probably doesn't help either. and she's gotten a bit more confident in herself but she definitely believes osamu can do better than her.
osamu also definitely believes she can do better than him, look at all those smart, well-off people she's going to college with.
at first atsumu just rolls his eyes at his brother but as he keeps insisting to not do anything about their obvious crushes on each other, eventually atsumu just goes "if yer not gonna ask her out, I will."
and if there's one thing osamu knows about his twin, it's that he'll make good on his threats, no matter how ill-advised they may be. he knows atsumu would do it, and if yachi for some reason said yes, he'd even be a decent boyfriend to her because they're good friends at this point.
so with his hand forced, osamu invites her to come over after closing time, and presents her with a more fancy meal not on the menu and eats with her. it's very date-like and out of the ordinary so yachi does eventually work up the courage to ask if there's an occasion for this. internally panicking thinking she forgot something important the whole time.
osamu blushes and almost chokes but he does manage to blurt out "would you like to be my girlfriend?"
it takes like a couple seconds to compute in yachi's brain so osamu is already backpedalling like "it's chill if not" but suddenly yachi gets incredibly red and stammers out nonsense syllables and just hides her face in her hands cuz she's completely overwhelmed.
osamu gives her a bit of time, then reaches out to take one of her hands and gently pry it away so he can look at her and see if she's alright
yachi just looks at their hands and thinks about how nice and warm osamu's hand feels and how he puts her at ease with his presence. and she nods and squeaks out an "I'd like to" and osamu smiles so brightly she feels like she needs sunscreen to protect herself from it.
then osamu presses a soft kiss to her hand and she almost faints
it takes them like three weeks from this point before their lips touch, and even longer to get any more intimate
atsumu meticulously documents this timeline to embarrass them at their wedding with it. osamu tells him "shut up you don't even know we'll make it to marriage yet" but like. they're gonna get married.
only when they've been together a couple of years and are both financially stable on their own and confirmed their life plans are compatible with each other, but. they do get married. it's one of the best days of their life. (and atsumu is there as best man to go "I told ya so" with the most obnoxious grin possible)
also they have the cutest kids and osamu is the best dad to them but idk maybe that should be another post this one is too long already