i can't believe my favorite "high schooler guy X hot loser degen woman in her mid-to-late 20s" manga is ending after 6 years, and yet its 13-year-old spinoff series about some weird-ass high school girl keeps going. such a cruel world
Let's be real, this series wouldn't sell well if not for the constant seggs. There's only so much Konogi-sensei can push the delusional attacks that Eroko pulls off in the early chapters, and once the seggs happened in C20, the story becomes extremely bland.
I'm glad someone actually pointed that out. You'd think it was verboten, with how almost no one would ever say such a thing about a female character whose looks are squarely within the (apparently) standardized limits prescribed (if not mandated) for manga/LN female leads.
Like I always say, if anyone can be beautiful the way women toss that word (or any like it, like "cute") at anyone or anything that makes them emote positively, nothing is. One can't say that Eruko and Senko are equal in that regard, just because she (the author is female, BTW) doesn't like the idea of some people with certain looks or preferences feeling excluded or otherwise negatively.
There's only so much Konogi-sensei can push the delusional attacks that Eroko pulls off in the early chapters, and once the seggs happened in C20, the story becomes extremely bland.
The story is more than just Eruko's secret identity and switch-flip behavioral changes: in addition to these, it's her romancing a guy ten years her junior--as a strange woman with a matchingly unorthodox perspective of the world and approach thereto that nevertheless wears her mask and fits in it. Such a story could go quite far, because it doesn't just end with Natsuki reaching legal majority--not in a First World full of dominant femininity (and consequent effeminacy), in which people can't help but seek out things to look down on in order to elevate their own egos.
For example, look at Leonardo DiCaprio: he has a reputation for seeking out girls much younger than he is--and it's justifiable, if you're honest and knowledgable. Never heard of him breaking the law that way, however, but people still age him down to place his interests beneath the age of legal majority or worse. Is there a point to this when everyone involved with him is a legal major? No, but it doesn't stop the gossips and the envious--just as Natsuki's legal majority wouldn't stop the eyeballs and pearl-clutchers, especially since women readily turn green when they see a truly beautiful woman.
Despite story elements such as the aforementioned example being capable of expanding the story, it's not necessary--Eruko is lovable and Natsuki is likable enough for it to keep going as is...under normal circumstances. In fact, the story isn't bland at all, with how many industry-standard trends it bucks: their romance is realized in chapter 9, marked with physicality via a kiss, when your average romcom can go over a hundred chapters without solid--or even any--romantic development.
Speaking of industry standards...Eruko herself is one major reason this story isn't bland. A girl who has her looks (large breasts especially, and especially when paired with long hair and gentle eyes) and character is simply not allowed to be a female lead in a romance--not without suffering some kind of negative portrayal (e.g., something to make her look worse, like a haircut for Character Development™) or being subjected to difficulties, which includes serious obstruction by rivals. Those rivals are usually either lolicon bait or girls who look like Senko or Ruka, who are--as I said previously--squarely in the industry-approved standard for manga/LN female leads. This is, of course, if the girl with Eruko's kind of character design isn't simply killed off somehow. (If you want an example of this, see Akame ga Kill!)
In contrast, the only thing keeping Henjo from being totally bog-standard is the titular weird girl herself--who is, as said previously, superficially average. (This is especially in comparison to Eruko.) Beneath that exterior is a strongly interesting character that can influence people indirectly, turning even people who know people who know Senko slightly weird solely by how she affects the lives of people in hers. Remove that, however, and Henjo has absolutely nothing that could set it apart from the countless romcoms that came before it. For example, what happens between Risa, Ruka, and Big★Mountain and how it's resolved follows the aforementioned standards to the letter; even how Risa "develops" (i.e., deteriorates) afterward is far from unheard-of.
All this is the case, and Henjo is at least up to chapter 137.