Kei was a bitch. Plain and simple. I was kinda put off with her liking Himari (i'm not a fan of same sex romance, and I actively avoid it), but probably wouldn't have cared if she treated Haruki nicer. That behaviour only works with tsunderes who like the main male lead, but treat them harshly, but with Kei, she just treated Haruki like trash, and was only nice to Kei. That just made her unlikeable. She could've still been a lesbian, and I wouldn't care as much, if she treated Haruki kindly, like a friend. Also, Haruki, was boring, but that's much better than Kei. Himari, I just can't hate. She might not have had much of a character arc, but she's just too god damn adorable and lovable. If the story centered more about Haruki being a shy shut-in introvert with agoraphobia, Kei being his childhood friend who doesn't like him romantically, but still cares deeply about him, and would actively try and help him with what he needed, and finally Himari being the person who manages to get him outside more, that setting would have worked in my opinion.