If you complain about this and that, maybe you should try the novel instead. It's more complete and elaborate by words rather than the manhua. Adapted works from novel is mostly like this, simplified so sometimes you find it a bit confusing and incomplete. I read the novel before the manhua so I found no trouble at all.
But yeah I can't sympathize with the people he killed. None of them seems human to me.
Is so mature she can't be bothered by petty idiots. True. Victims don't have to act like one because they're already are. People take pain differently, and for Dan ah there are more concerning matter of how to spend her life without losing her friends so yeah. Being bullied is sad, but she knows she's loved by people who loves her. That's enough.
What about the other pairing? Do they have a story too?