I don't think it's inconsistent with how she was written at all, I'm just saddened that it narrows the possible trajectory of her character by starting to eliminate my preferred reading of her actions. My previous read had her as the kind of person who would reject the characterization of people as 'dark' or 'light' as something that entirely belonged in Hikari's naive world. She didn't hate the nickname Yami because she agreed it hit too close to home, but because it "wasn't even wrong," so to speak - she resented people conflating her character with her circumstances.
Yeah, she can be read as being cool and edgy (in the "underwhelmed/over it" behavior sense) through her early interactions with Yuu but she never comes out and says that's what she's going for - we're left to infer that from her actions. The insight we get into her thought process is mostly focused on accomplishing a series of short-term goals. I preferred a reality where that was less of a "leaning into a role" thing and more of a "she's emotionally burned out and has nothing left to give" thing. She didn't think of herself as a dark girl or one tainted by darkness, but as a normal girl denied a normal life by forces beyond her control.
Once she and Yuu were together, though, my sense was that she wasn't actively trying to be cool at all - she was a little distant in what she shared with him less out of "not wanting to appear weak" and more out of the fact that this relationship was the one place in her life where she COULD be weak and uncool and normal, and she had to compartmentalize the hell out of her life to achieve that. Throwing that away was development toward self-sacrifice from self-destruction, even if it was maybe still somewhere in between the two.
Yeah, her whole "sex == defilement," thing is consistent with being a shitty edgelord, but I was reading that more as rationalization for her own self-destructive pursuit of an un-numbing pleasure ("carve scars into both our hearts") on the worst day of her life, than a legit premeditated motive based in self-pity. I was hoping that giving her a tragic backstory was showing that she came by her realism honestly, and that she would be growing up and out of the worst of it, but never internalizing the idea that her experiences contributed to a "darkness" that needed to be fixed.
Mostly I guess I don't want to see either girl's development sacrificed on the altar of that parallel structure, because I actually really like this story and I don't want to see it invalidated for a gimmick. I'm even fine with them meeting in the middle - Hikari was written from the jump as more concerned with appearances than actual morality, and people forget that she's straight-up deceptive in like almost every chapter with Yuu, because it's in pursuit of adorable childhood friend/crush hijinks. I'd love to see her develop beyond a collection of tropes, and she started to do that walking to school with Yuu the morning of the current "futuremost point in the timeline." Ayami being edgy feels like a reduction in the overall complexity of her character, and thus kind of a waste.
Once you go down the road of each lead containing dichotomies, nothing's off the table anymore (e.g., not forgiving Aya, like you said) and anything can be explained away moment-to-moment. That would be lazy and I think this series is better than that, although these past two half-chapters didn't quite hit for me.
