After dropping this title and occasionally returning to see if there has been any improvement in the writing, time to share some thoughts. Let's discuss Nagi's (the MC's) choices.
Sachi, (Nagi's younger non-blood sister):
Let's begin with the younger sister. Clearly, from chapter 1, she's had a mild case of bro-con crush on Nagi. The thought of Nagi moving out and away brought tears to her eyes. This was a painful thought for her because, well let's face it, she is the youngest of the four main players (she's what... 14?). I cannot expect her to respond to heart issues as Erika/Segawa/Nagi would due to this important difference in years where emotions are a tougher thing to sort out. Some of us, in this thread, are kinda pouring a bit too much hate on her. She's younger. Therefore, more childish. If we could age her up to her match the other three, we'd get more refined responses and thoughtfulness.
A) A part of Sachi doesn't want to lose her brother.
B) Part of her has that old, lingering bro-con crush.
C) The competition is stiff with Erika/Sagawa, she knows it, and she's none to happy about it.
I agree: a healthy brother/sister relationship between Nagi-kun and Sachi-chan would have saved this story from my point of view (his "little sister" may have been an interesting ally). But adding Sachi into the Possible Candidates List is a tired old trope hauled out by overworked and underpaid Manga writers who likely feel pressured to "keep up the status quo."
Erika, (the gal the MC was switched with at birth):
I suppose she can keep maturing. But a spoiled rich kid who has difficulty boiling water for tea, hates studying and has made the lead's life difficult by bossing him around shouldn't even be considered marriage material, regardless how much Nagi's bio-dad thinks this can be the case. Erika has shown some signs of wanting to mature (blandly tosses confetti)... but why? Certainly not for Nagi's sake: she's barely a blip on his radar. Oh, yes; we all get the giggles (well, I don't) when she emerges wearing some cute cosplay outfit according to how she reads the room: "Doctor Erika"," Erika Holmes", and so forth. But those giggles won't sustain a long-term relationship.
A) She's an Internet Idol of her own making. That alone speaks volumes in terms of any opportunities with the MC.
B) She has nothing to gain by capturing Nagi's interest, other than satisfying a "dad" who's not even her real father!!
C) Nagi has little to gain from continuing the engagement with her.
Let's skip ahead, and look at...
Nagi himself:
Like typical MC's in a comedy Harem trope, Nagi is late to grow a spine. Keeping secrets, dishonesty, the inability to confront, (etc.), form too much a part of his character. Erika may feel "forced" to do what her adoptive father wants. But Nagi, our hapless MC, is under no such obligation. Confronting his bio-dad to state his refusal to participate in the deranged arranged marriage nonsense (from some by-gone era) would go a long way to help the MC to stand on his own two feet. He has little to gain from these adventures if he succumbs to a twisted parent's will (sadly, all four parents have ganged up on Nagi and Erika).
A) Nagi, our MC, clearly doesn't want Erika. Good for him. He may be "nice" to her, but heck: he's nice to just about everyone.
B) He isn't cool with the idea of settling down with a girl he sees as his "little sister", since he hasn't a sis-con bone in his body.
C) Struggling for the girl of his choice will build more character than having some gal tossed at him like a bone to a dog.
Moving on to...
Segawa (a random gal at school the MC has so little in common with, he can barely speak to her--a crush, basically):
My least favorite character. She's also engaged. Yes, Segawa's is an arranged marriage--and you'd think that the same argument could be said of her that I applied to Nagi. HOWEVER.
A) In Segawa's case, the arranged marriage wasn't something thrown at her "last minute" as in Nagi's case. She knew about this a lonnnnnnng time, hence her long list of rejected suitors. The degree to which Nagi takes his arranged marriage seriously compared to how Segawa does (this also being part of her religious up-bringing) is vastly different.
B) Culturally, no one would blame Nagi for skipping on a deranged arrangement from twisted parents. But Segawa is not in the same boat.
C) Also, though it hasn't come to light yet, we have no idea what Segawa's fiancé thinks about this. Is he insanely jealous? Is he relieved? Does it matter, him being caught in the same depth of religious/cultural demands as Segawa?
Clearly, Segawa's mom takes a dim view of her daughter hanging out with Nagi. So, the similarities end at the words "arranged marriage." My impression is that Segawa has no say in the matter, whereas Nagi does, and isn't man enough to do so.
The Parents ... ohhhhh these sick, twisted parents:
I wish could fully unpack my thoughts about these four overgrown delinquents. It's enough to focus on Nagi's biological father. Where does he come off imposing something as personal as getting married on a boy he has never laid eyes on. That's hubris and arrogance the MC should never have acknowledged or respected in the first place. Our MC should have turned and walked away from the bargaining table without a word, without so much as acknowledging his bio-dad. Worse still: the MC's adoptive parents chime in their agreement. Seriously. Before considering their own son's thoughts and feelings, they were already counting potential Yen they'd receive through a marriage with a rich family (admittedly, not openly stated—but it's suggestive). Such casual betrayal. I could say more but, I should move on to my...
Final thoughts:
I see utter failure in all three bridal options. But I suppose that's our writer's long-term plan: to present a situation where NONE of the MC's choices would ever make sense, maintaining a train-wreck of a balancing act. What gives a writer boldness to get away with awful writing? it's a Comedy!!! And there's nothing like the Comedy stamp on a Manga title to legitimize the WORST writing.
Hope for future chapters
If Nagi were to perform a "relational Ctrl+Alt+Delete", starting with Bio-dad (his birth father who seems to be the mastermind orchestrating this nonsense), I'd hop back on this story full-time and rate it 10/10 in a heartbeat. However. We all know that ain't gonna happen. Cuz, it's a Comedy! And what's a RomCom without a bumbling, spineless, dishonest MC chasing and being chased by all the wrong gals? Honestly, until our MC steps up to the plate as a genuine Chad, ain't nothing worth reading here.