Nah, she was like this from the start. She's a sociopath but, so far as we've seen a harmless one. It wasn't till Kitami started bringing his serial killing to her door that she even did anything screwed up.
The reason it seems like she's gone nowhere character wise is because... she has gone nowhere. You have to actually exist in the story for more than 2 seconds at a time to have character development. But, the author bait and switched us with who the mc was and relegated her to background character A. Since then the authors done jack all with her.
I like Nomamoto's sociopathy and thought it'd be interesting to play into it. I'm curious where the story is going. But, I don't appreciate the mc swap up. I really just don't care at all about Kitami or his misguided vengeance. So I'm really hoping this is just a long character arc for Kitami to get him out of the way before bringing Nomamoto back. If not... well, can't say I'll be able to maintain my interest.
To be fair, her type of mindset is fairly hard to write as the primary protagonist. Stories are (usually) built around character development, and these kinds of characters can be limited in how they can develop (at least, to the extent that protagonists develop) without radically changing their mindsets and characters. They're interesting, but hard to write as
the starring role.
They work best when they have other characters they can play off of who can react to their sociopathy, which seems to be Seiran's primary role since they're trying to hide the alien murder from the public. That, and he enables her and encourages it, which is also pretty interesting.
I think they do have equal roles in the story, this arc is just heavily about Seiran and his past. It's also exploring the whole morality of killing aliens to further highlight how messed up Nomamoto is (see:
everything she said in this chapter), and showing off the imbalance in their partnership. She doesn't specifically NEED Seiran, and he knows it. And now he gets to confirm she's even more of a psychopath than we already thought.
I really like her character for the record. It's really rare to see this sort of crazy apathetic character in a lead role, and especially as a
female lead. She's not bloodthirsty or cruel, she's just super selfish. It's a fun take.
Related: maybe that's why this series reminds me of Freesia despite the tones and plots being radically different. The protagonist was kinda similar to Nomamoto, in that he was very mentally screwed up and had no real moral qualms about murder. He was just a more somber, quiet and gloomy type, so it wasn't as apparent as with Nomamoto's casual and vocal disregard for any life besides her own.
