The fact that you see “a heroine’s purity or chastity” as a “flag that she’s going to win” is unironically part of what most men (and to a horrific point, many otaku) want in a woman.
While women generally tend to fantasize about being their man’s last women and partner for life, it is often said that men tend to idealize the thought of being a woman’s first and only.
As for the Japanese otaku side of things, it should be relatively well known that they value purity on an extraordinarily high level. It is to the point where some people could find it laughable that they get disgusted that their 2D waifu would ever interact with a male character, especially in female-only cast slice of life shows. An example of this would be Lovelive fans getting mad at the Granblue Fantasy crossover collaboration to the point that Granblue Fantasy had to intentionally write the event without a single male character in-game appearing once.
On the horrific side of things, it leads to otaku mass slut-shaming their favorite idols or voice actors upon hearing they aren’t pure anymore. This can take form in destruction of their own merchandise/property, to outright stabbings. Because of this, the purity of fictional characters is so heavily protected. A cheap example I can think of off the top of my head is Sword Maiden vs Priestess from Goblin Slayer. I have seen no shortage of people, jokingly or not, claim they wouldn’t want a goblin’s used goods. A more obscure one might be idol anime crap like lovelive and idol masters. Weirder ones might be Hibike Euphorium or Love Lab, where people prefer the characters be lesbian lovers than pursue relationships with men.
Incels, or involuntary celibates, is a term that was warped into an insult towards people that are so undesirable, that they are literally single virgins and not necessarily by their own decisions. Incels, or Eugenes, or whatever you want to call them, tend to share those levels of extreme idealism and obsession with virginity in women. Incel is a term mostly used by normies, but not ones you’d ever want to associate with.
But yeah, to sum things up, using manga tropes to learn lessons is probably going to be as good as using romcom movies as dating advice. The tropes are common in fiction, but realistically terrible. I really like that the author himself has no intention of stopping Kaguya and Shirogane’s story right after confessing, like how so many stories end right after the main characters start going out, sometimes without a kiss, or even holding hands, showing no effort to go to the next level and actually displaying their lovey dovey life as couples.
Aka’s a kind of person to subvert expectations— to me, him claiming Tsubame once had an ex was a bold move. I can see a lot of people that use Ishigami as a relatable character having a harsh dissonance with going after a person that might not be as chaste as they are.
