I've read a few arcs in the Web Novel version (it's quite different to the LN and this Manga) and yeah, big ones aren't that desirable lol
In this world, Medium is Premium.
So this girl was conscious of her 2
big insecurities and her doutei nerves also got to her.
This reverse chastity world is kinda more fleshed out in some of the ways it reverses things. Like guys still do sports and aren't zesty. I think guys in this world are more reserved than girls in ours.
There's actual differences in preferences in this world, not just manly girls and feminine boys, like if a girl reads lewd manga they'll think that the MC is the fictional 'lewd jimio' type, not just a man slut.
Girls like muscular and tall guys, some like lean guys, some like big biceps, and they're not afraid to proclaim it loudly.
Guys still like beautiful, lady-like girls but they're more reserved about it, and like how some girls find very buff guys to be off-putting, guys think the same of girls with big boobs in this world. So guys in this world actually judge based on personality and looks too, we just don't have the perspective for it here because the main character is 'weird' and his friend is super reserved.
Basically most of the standards remain the same, the vocal ones just reversed and guys have toned down libido so they don't actively seek the sensual parts of women.
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That's one of the issues I always have with these reverse chastity concepts. Everyone dresses exactly like in our world. It makes no sense!
One example:
Skirts evolved as a way to hide women's legs (once they started becoming gendered clothing), then became a way to show them off in the 60s. There's no biological imperative towards skirts or pants, so it stands to reason in a chastity reversed world that the uniforms should be skirts for guys and pants for girls.
But why would guys wear skirts in this world though? This reverse world is supposed to be almost exactly the same but only chastity and some morals are different.
It's not like pants don't exist to hide legs or something.
In this world men still do work that men should. Wearing skirts would be annoying for guys in physical occupations throughout history. (Even women that worked in our history wore 'men' clothes because it was practical.) It's not like the men here are doing house husband work or were noble men that just socialize, drink tea or try to be in fashion... and even if men did do that—because that does happen in history—they'd wear clothes fitting for their looks and station, not wear impractical skirts or dresses that would make them look awkward or even ugly. Aside from looks, a lot of fashion was made for practicality too and, unless they wore kilts or robes in their culture, they'd wear something that looks good and they can wear for work.
Even in medieval Japan where everyone basically just wore the equivalent of robes, the style differ based on what looks good. Women's yukata had longer sleeves and cut longer to accomodate decorative folds, while men's had shorter sleeves and cut at the ankles. And they adjust them based on what they do, they would tie back their sleeves or wear loose robes, they don't wear clothes differently just to contrast the other gender.
Guys wearing skirts and girls wearing pants for their uniform doesn't even connect to the reasoning of why they were worn—it's because unlike a yukata, this type of skirt were easy to move around in (for gym), they were easy to make and they weren't too fancy. They were also based on the British Royal Navy uniforms in comparison to boy's uniforms that were based on the Prussian army uniform from the 1800s.
So, in a chastity reversed world, it's more reasonable to think that both would have worn pants up until revealing clothes would be normalized and then guys would be okay with wearing shorter sleeves and showing a bit more of their arms and biceps. Also, in reality a school girl's skirt isn't as short as in manga and anime. They're supposed to be below the knee length... but some do fold it up to show more leg. The equivalent in this manga would be guys folding up their sleeves or loosening their shirt buttons.
Actually, if men in this reverse world did really want to objectify themselves and wear things that make them more sensual to the opposite sex they'd be wearing platform shoes for height (maybe heels too from the horseback riding days), tank tops to show off their biceps and tight fitting pants to show off their thigh muscles and their bulge, not skirts that show off legs.
Related to this, in the last chapter the MC saw her panties, the moment wasn't explained in this manga but she actually didn't seem to mind showing her underwear... and those were kinda like Calvin Klein style, very plain panties and it was also shown in this chapter where she wears a sports bra. The girls don't actually bother with fancy, girly underwear—they just wear whatever like how men do.
Also not (yet?) in this manga is when the MC was getting dressed for school his mom barged into his room and was so flustered because he was only half dressed.
Another thing not (yet?) in here is that MC saw a spicy telenovela and he saw that the guy that was being seductive and pinned down by a woman in the show wore a tight tank top (very suggestive in this world).