@Pachka84
Again: why are there so many people who can't swim in the fiction of a country that is made up of islands?
Being bad at swimming is a common character trope. Don't really need to dwell on it, it's just an easy weakness to give people so they can be taught how to swim by their romantic partner in these sorts of romcom deals. There are people who can't swim in Japan, because there are people who can't swim everywhere, it's just probably not nearly as many as you might think based on impressions caused by manga and anime (the number of characters who can't swim in everything you've ever read or watch is still going to be a drop in the bucket as far as Japan's total population goes though, to be honest).
And again: why are the ones who can't swim always girls with black hair?
The hair thing is just your weird obsession with some pointless thing you fixated on. No need to dwell on that either, it's just the "new car effect," isn't it? It's like when you buy a new car, and start seeing that model of car everywhere. The number of people driving that model of car near you didn't abruptly change or anything. You're just noticing it because it's already on your mind, you're unconsciously looking for and focussing on them. I saw you not commenting at all after thoroughly complaining about this light hair vs dark hair thing on that Centaur SOL series whenever the opposite of what you were talking about was happening.
Here, you're looking for dark haired characters in these positions you keep commenting about everywhere I've seen you and then act like it's always only them. There are plenty of light haired characters (not just blondes, because half the characters I've seen you call blonde now actually had light brown or even random non-natural hair colors when you actually look at the character in color) that are terrible at things or get shat on by other characters who also may or may not have dark hair, because that doesn't matter nearly as much as you seem to think to anyone else including the authors and artists. The only real pattern there if there is one at all is commonalities in personal preferences of content creators. It's not some weird conspiracy to tear down people with particular hair colors.
And why are the assholes blonde girls?
Blonde hair in Japan is often attributed to delinquents, so yeah a lot of blonde haired characters are going to be assholes. Delinquents aren't generally supposed to be the nicest people, that's why they're called delinquents. Nothing special there, you probably already knew the answer to this question when you asked it but you like being a weirdo about hair colors.
And why don't they get their come-uppance?
What exactly did you think the older brother showing up and looking ominous before the scene changes to all the delinquents not even being there anymore was? A polite conversation off screen? He, a dark haired character (shocking!) chased off the asshole "blondes," (who may or may not even actually be blonde, they're not in color to begin with). For all we know they had light blue hair or something, because manga.
Anyway this is probably the last thing I'll ever say to you on this site. You're either trolling with the weirdest thing in the universe or actually this weird and I just don't care anymore either way now that I've vented a little.