Huh. She's a bit of an interesting character so far, both obsessed with his purity but also wanting to protect it. I'm almost certain it's because she sees herself as the opposite of him, completely dirty and tainted.
If true, that would be an interesting twist compared to the last arc, because it would mean this character has some kind of inner foil.
The last one didn't have any character-specific foil. She had general foils from things like the law. The complexity came from the
external impact. The story challenged the status quo by looking at the fallout of a Yandere destroying something society, or the narrative, usually treats as sacred. The tension was about the
reasons and
consequences of that destruction.
If things are as you say, the complexity now turns
inward. It is no longer just about the destruction of an external concept, but about a character waging a war against themselves. Her obsession isn't born out of entitlement.
However, we still have another version of the "necessary evil" justification that is implied all throughout this arc. She needs a monster to protect him from, which she has obtained by measuring his purity. But what happens when she finds this "monster" in his mother? Will she see that the purity she cherishes in him is its own kind of stain? Will she ironically "sully" him like herself to set him free? To make him clean "again", as if to fulfill her mis-perceived understanding of him and ultimately dolling him in her own fashion, just like his mother?
If so that would bring us back to square one of the first arc where the same kind of tensions lie in the external impact. She simply inherits the crown of the "monster", making this a masterclass in tragic cyclical storytelling. And yet in both arcs I think the monster, the deconstructing heroine, is ultimately the far better choice!