@Nihilist1
I know you already got convinced to try reading it again someday, but I want to say something too.
It was never her intention to be a bully. Believe it or not, the way she behaved in those first chapters are very out-of-character for her. But she did behave that way and the question is "why"?
Her first words to him were actually positive. She saw his manga and said "wow! Hey, did you draw this?". She was impressed. Later chapters show that she's not so easily impressed when it comes to boys. She straight up says she finds boys so boring. And typically, she's very standoffish and defensive when interacting with boys. She doesn't act that way with Senpai though. She starts "bullying" him. Something that she wouldn't normally do.
The fact is, a boy did something impressive for once (without bragging about it either) and it excited her. She caught some feelings for him. However, she's young and inexperienced with having a crush for the first time. She wanted his full attention and didn't know how to get it properly. So she did the equivalent of a little boy hitting the girl of his affections. You saw the results of that; he ended up crying. And on the outside, she "seemed" happy that she did that to him. But there's an extra page that you won't see on here that shows her alone and feeling like shit for how she acted.
It pretty much repeats in chapter 2 because she didn't learn the first time, and again there is an extra page where she is regretting her actions. I can find those two extras for you if you want.
As for not seeing how toying with him brings him out of his shell, well... He was anxiety-ridden to the point he could not interact with girls. When Nagatoro started "bullying" him, he just tried to shut down until the problem goes away, like usual. She didn't go away, though. She kept getting in his face and demanded his attention. It became reality that he can't just ignore her and was forced into confronting the situation. Over time, it went from being a horrifying experience to a somewhat annoying one. That's a huge improvement for him. He's now capable of talking to her like a friend, hanging out with her, and even touching her without having a meltdown about it.
And that whole toying with him thing is just a weak facade to hide her feelings from him. Every time she's saying or doing suggestive towards him, she's always blushing and sweating. She's always on the verge of losing her cool. She just knows he'll lose his cool first and that's why she does it. There are times where he says something unexpected and it trips her up.
Please definitely re-read it with these perspectives in mind.