I blame fandom flanderizing her, and also KK*TA. People are more attracted to characters that resonate with them, so whatever crazy shizo weirdo thing Koishi has become attracts weirdos. I personally know only one koishi fan and yes, xhe is weird
She's an entry level 2hu and very commonly depicted in memes and porn but in actual 2hu she's a bit of a nothing character so many albeit not all "koishi fans" are new and younger
I'm pretty sure this horse was beaten to death a long time ago though
flan and koishi are the biggest secondary bait characters but all of the th06 characters are like that so it makes koishi extremely standout with secondaries suwako is not as much of a secondary bait character, but something about being an extra stage from an easy game makes them borderline secondarybait
the only EXTRA boss that isnt for secondaries and never will be is the evil eye sigma male