Hiiragi is insufferable. I can't stand chapters with her. Why does she hate her sister so much? Tsubaki was just being happy and giggling a bit! How am I even supposed to care about her and Utsugi when she is such a bitch? Utsugi is better off without her, poor thing.
I could do without her storyline until redemption chapters or something. As to why she hates Tsubaki, I think it's been shown it's because, despite being meek and shy, Tsubaki still functions better than her (is smarter and accomplishes more) and continues to put in effort, giving Hiiragi (who struggles and clearly has no friends) a huge complex that she takes out on her sister. I think she also dislikes that Tsubaki is doing well without her.
Tsubaki is such a cute cinnamon roll. The two whose had issues with her clearly have deep issues of their own (the sister's inferiority complex and Nakatani's jealousy, but at least Nakatani's still a good person and isn't emotionally abusive like the sister).