Even though she is naked, its not emphasized. It is not the importance. The pictures you linked are SUPER tame compared to the other characters listed. (Plus, again, when you search her, you get pictures of her with her mask and blood vs naked slime pictures)
I know, but that doesn't mean she wasn't made to appeal to men in a similar (just tamer) vein as the others.
Pieces of a puzzle coming together... You know, I have been curious about this "phenomenon" for a long time. Now thanks to this forum and the people here, I have a good chance to reveal this mystery I'm fascinated by just how much the audience LOVE the characters which I mentioned in OP. Whenever it's a cosplay party or Halloween - a lot of people are getting dressed up like Harley Quinn, Himiko Toga, etc... People really love them, they really enjoy performing the role of those characters (Especially Harley Quinn, in terms of popularity she broke all the records. This character created a cult. There are people who literally worship her, no joke.) I knew that it was never about appearance. It's about their nature and behavior. People seem to like danger and unpredictability...
Complexity? I don't know all of these characters but out of the ones I do, they tend towards complex characterization where their motivations aren't entirely a matter of "good or evil", which gives them potential to be more than they appear. See, I never really liked Harley Quinn until she started to break away from the Joker and become sort of a self-realized anti-hero. (With occasional purely heroic impulses.) Aside from the generally optimistic theme of restorative justice, that just felt like the natural evolution of her character, which I think is what made it so gratifying. Remember, this woman started out as a professional psychiatrist - she was originally a person who wanted to help people - before the Joker got to her. And even at her worst, she was motivated by her love for the Joker. She was ultimately driven by positive feelings, no matter how misguided those feeling where. At this point Harley is basically the DC equivalent of Deadpool, another character who is also mainly interesting because he tries to be a good guy (or at least not a bad guy) while not entirely understanding what that means. Toga, likewise, appears to be mainly driven by her passions. She's an idealist and a romantic, straight up falling in love with the hero. Her main problem is a twisted world-view resulting in basically having no real sense of morality. This makes her a villain, sure, but there's a distinct tragedy to it - she gives you the impression that she just doesn't get that she's a villain. Like if you could just make her understand the difference, she'd turn around and be one of the good guys. I guess the point is, these characters aren't inherently locked into their roles as villains. There hope for them.
^^ Reminds me of Catwoman and Magneto, who straddle the line between good and evil and come down sometimes on one side, sometimes on the other. They seem to be amoral, or in the words of Fred Nietzsche 'beyond good and evil' (like his Ubermensch). They have their own internal motivations and care not a whit for society's hidebound ideas of morality and altruism.
Meh. Himiko ranks 10th on this poll: https://www.cbr.com/my-hero-academia-fan-favorite-characters-ranked-myanimelist/ The frog girl and Ochaco are more popular than her.
The skin-tight clothes are from the early days of comic books. Normally clothes have to be drawn draped on a body, so they went with skin-tight costumes so they were able to knock out comics more quickly by missing that stage and just colouring in what is essentially a nude. We still have that today partly because it's sexy, and partly because skin-tight is now traditional for superhero costumes.
If you do a little research, you will find that Toga is the most popular character in My hero academia.