I read the first chapter a few years ago when it came out and ran away in disgust. Now I'm here, after binging the entire series, re-reading it twice, reading all 100 pages of comments (yes, even those saying Ayako had drugged Asuka and molested her), supporting the author on Pixiv and buying all the issues on Amazon. God damn… Taiyaki is a goddess. I had never seen such a beautifully built trainwreck of a relationship.
Okay, let's start with the obvious. Ayako needs therapy ASAP. It's obvious that she can function as a productive member of the working class, but in the affective realm she has the maturity of a child. I believe the reason is that Ayako may be autistic and had a horrible childhood. Maybe I'm projecting here, I'm autistic myself and also a survivor of child abuse from 6 to 13 years of age. The first few pages of Chapter 15 describe my own experience and inability to understand my own emotions so well that it's uncanny.
However, I don't think the author will take it that way. Therapy tends to be an unsatisfying way to resolve an inner conflict in fiction.
So, here are my thoughts:
About the strange predisposition Atsushi talked about in Chapter 16, I think it might be 'indifference' on a massive scale. Ayako was known to be uninterested in other people and to be unable to smile. Try talking to someone that's physically there, but doesn't smile, just stares at you or gazes somewhere off. It's unnerving. I can see how it would be difficult for a person who's basically expressionless to live day to day. By pairing with someone as confident as Atsushi, it could somewhat alleviate some of the issues. The reason why Ayako married Atsushi was to have a family, which is something she desperately wanted. (This is purely speculation, of course.)
Through Akira's kiss, Ayako will realize she feels absolutely nothing of the rush of feelings and arousal she feels with Asuka, which will confirm that she is in fact head over heels for her daughter. It seems strange that someone her age would've missed the signs being thrown at her in every direction, but I think this is the first time Ayako has been in love. Some readers have theorized she's a closeted lesbian. I don't think that's the case. I think she's demisexual, someone who only feels sexual attraction after forming a deep emotional connection. And let's remember that Ayako doesn't seem to have much of a history forming deep emotional connections… The only confirmed case is, in fact, her daughter.
I hope they don't go all the way immediately after this revelation. I want them to be together, but for the right reasons. I suspect Ayako holds an immense amount of self-loathing and guilt. Notice that she blamed herself for Asuka falling in love with her, and before running off to Akira's she remembered scenes of the blissful times she spent with Asuka only to then think "In the end, for someone like me, wanting to be a family with someone was just a long dream." The poor woman thinks that she doesn't deserve a family… That's heartbreaking.