This doesn't make any sense. We still don't know why the heck Kei hate the stupid MC (most likely something silly) but why the heck would you be make her act like a jerk to the brother of her love interest? Man, this manga is just a mess and introduced so many other characters all in one go but keep focusing on Kei alone. There have been pretty much zero character development for everyone, just Himari got friends and is now kinda close to her brother, Haruki is getting pushed around by Himari's pace, and Kei having the romance focus, the others just exists.
Seriously it's like this manga is shifting from Himari no Mawari to Kei no Mawari. Next thing you know Haruki's parents divorce ,Himari is forced to go with her mother, Kei confess and get rejected, fall in depression and become a loner like the guy she hate while Haruki decide to act more cheerfully like Himari did and becomes the real winner.