That's intentional. The work is very good at showing that people aren't strictly black-or-white. Kanae is a victim just as much as she is an abuser, as is this girl.
Teenagers are fickle and their loyalties change with the wind. No one here is unequivocally bad and they all operate from some internal mechanism or reasoning that come into natural conflict with one another, which ultimately escalates into tragedy.
I'd argue that its similar to other works like
The Great Gatsby in which most characters are unlikable, and intentionally so as to further the themes that the author is trying to compel. For instance, Nick Carroway, the narrator and the lens in which the audience views the world, says at the beginning of Gatsby that the only one that turned out right at the end was Gatsby, but it was what preyed on Gatsby that caused his downfall.
Something similar happens, if you recall, at the beginning of this story in which we see our narrator (Hiroshi) getting arrested after (supposedly) killing Kanae. I would go as far as to argue that both of these works are pointing to the same fundamental theme of shallowness and the fickle nature of people, and how such forces lead good people to ultimately do bad things. Each of the characters so far do bad things because of this theme and the pressure from others to commit them. Narumi doesn't want to participate in the gang rape of Ichika, but the woman he loves is watching him and pressuring him to participate. Ichika bullied Kanae because her friends were egging her on into blaming Kanae and turn as soon as she (Ichika) has been gone from school for some extended period of time.
Each character does wrong deeds for a cause they justify to themselves internally, when we, the audience, know that that line of reasoning is flawed or incorrect. The author isn't just making torture porn or trying to have us witness suffering for the sake of sadism or masochism, but to demonstrate her point and emphasize the tragedy of the situation and circumstances, and that if everything was just a little bit different, and if the characters took slightly different actions instead of falling in line, all of this could have been avoided.
@psgokhan @Harem_Sovereign @semon_demon @nightvolt