I know people say she has a crush on Kase, but in order to maintain that crush she's ignoring the fact that she knows Kase has a significant other, and she confronts Kase only with petulance, aggression, and bullying.
Fukami knows Kase has a significant other?? When did she find out???
Chapter 7, although Fukami currently assumes it's a guy.
This is why I think the blame for this amongst the fictional characters has to land mostly on Fukami's shoulders. Knowing this, she doesn't care, and demands this race like a sociopath. Doesn't matter Kase has a special friend, Fukami wants this thing––she only feels Kase's being unfair because Kase isn't giving her exactly what she––Fukami––wants. She's been entirely quiet and non-communicative the entire time she's roomed with Kase (and Kase, while not around sometimes, always makes time to talk with Fukami), and now she blows up and throws a tantrum she frankly has no business throwing in the first place.
Kase, meanwhile, goes out of her way to accommodate Fukami's feelings––and Fukami's response is bitter, as if Kase's done something to wrong her. But this wrong never occurred in the first place. Fukami is totally out of line here. I've heard that in Japanese argumentative traditions the point will often go to the person who expresses the most convincing passion for the subject (not that it's unheard of in the west as a way to win an argument, but apparently the method we prefer to employ in the west––of arranging and directly deploying our best argumentative points––has very little purchase there). Presumably this means that more people are moved by that person's feeling for what they are saying at the time. I suppose this could be what is happening when Fukami faces down Kase. Still, Fukami is entirely in the wrong. And no wonder Kase and Yama react the way they do. Fukami makes it literally impossible for Kase to find any alternative solution to the problem––she has one way she wants this to be resolved; she wants to beat Kase-san––and in doing so, take over her life, I guess. This is such a gross character. She's been a jerk for ages, but in this end game she is really despicable.
In fairness vis a vis my previous post, I suppose none of the members of the team do much for Fukami, either. Both girls are left out to dry here. Fukami has literally no one to talk to. On the other hand, she also chooses not to talk to anyone about anything she's feeling. So I still have no sympathy for her. She has a wretched attitude, in which she seeks to bully others for her own, self-manufactured unhappiness. The annoying thing is, I kind of want a bully's end for her storyline, and I'm pretty sure it's not going to happen. I don't want to feel any extra sympathy for this character––she's blown through all the guardrails for me, and is not just a creep. But I'm sure there will be an understanding at the end of this, where Fukami learns something important––something she really could have learned by thinking about things and talking them out with other people, instead of just internalizing––but that understanding will be supposed to ennoble her in the readers' minds. Not appreciated.