I'm not getting the only one thing. Why couldn't original B-ko stay with clone A-ko? They are already dating and stuff, so what's wrong on wanting more and go further? What's the drama about making appearances and growing apart? ._.
Some people just can't let themselves be themselves and live up to their desires, I guess. They are liars who want someone to make their lie come true. And I don't get it
Assuming that the original B-ko is the one with the knife and the clone A-ko is the one who claimed original A-ko was the braids one, then it's quite clear to me that clone A-ko basically didn't have actual romantic feelings for B-ko, unlike the shut-in original A-ko who was swept off her feet. The line about "her feeling of liking B-ko was a little different than what B-ko was feeling" is usually a shorthand for romantic rejection: "I like you, too, but only as a friend." It's sadly a very common story.
My interpretation is that the "Kodoku Syndrome" is a metaphor for the postmodern understanding of personal identity, which means that the distinction between "originals" and "clones" is wholly artificial. Each of them represents a different facet or mindset of an entity we call "person", and none of them is any more deserving of being the dominant one in public (that is, snuffing out all others) than the rest.
If you instead read the story under the assumption that all A-kos and all B-kos are the same physical individuals, respectively, then it goes something like this: A-ko grew up as a shut in, then at some point, mustered strength to go outside and to make friends - in other words, her new outgoing personality supplanted the old shut-in identity in public, but unlike B-ko, she did not completely abandon her old self in some ways. In any case, this new outgoing A-ko met and charmed the equally shut-in schoolmate named B-ko, who, in a classic manner of teenage-hood, began suppressing her desire for B-ko out of fear for their hard-earned friendship. The repeated murder of "clone B-kos" is thus an extended metaphor for the constant self-mortification carried out by a person who suppresses her true desires on daily basis.
The whole "NTR double-date" scene in chapter 2 could be read as a really confused date between A-ko and B-ko, who, at first, showed each other the different sides of themselves who did have massive chemistry with each other, but then A-ko refused to maintain her shut-in facade and made it clear that she cannot love back the B-ko who cannot move on from her self-denying ways. Which doesn't necessarily mean that A-ko will fall for B-ko once she does move on, but this is strongly implied at several points, which have already been discussed here. In the end, I prefer to think of the conclusion as a happy one: there was no murder of the original B-ko by an impostor, it was simply her experiencing a catharsis and emerging as much more well-adjusted individual who does have a chance with A-ko, judging by the latter's reactions.
Wow this makes A LOT OF SENSE all of a sudden. Thanks for this really thought out explanation.