This is not really a Harem. The only person who has feelings for the Male MC is Otobe, the FMC wants to remain friends with the Male MC and is attempting to avoid 1-on-1 hang outs since she doesn't want the MC to confess to her resulting in a shattered relationship between Otobe and MMC.
ALSO, dont forget that Hebikawa DOESN'T actually like the MC. She just wants to see the dark side of the pure Kusunoki since she believes that all cute girls are evil like her. She is envious on how Pure Kusunoki is and wants to see her suffer. Hebikawa is just trying to NTR the FMC and abandon Keisuke (MC) right after.
This is more of a psychological harem than a romance one. One is trying to Salvage the relationship "keep it pure", the other is trying to crumble the MC and FMC dynamic, and the other wants the MC disregarding the negative impact it could insue within the relationships.
Most mix gender friend groups in real life fail because friends develop feelings, break up, get envious, or become distant. We are witnessing this crumbling occurring, nothing about it is cutsy, romantic, or entertaining. its lowkey psychological horror if you really think about it. If the MC choses Hebikawa, then the FMC will isolate herself like she did in the past and the MC will be tramatized with girls since he was bamboozed again. If the MC chooses Otobe, the FMC will lose her best friend who helped her overcome shyness. If the MC choses the FMC, then she will lose Otobe. This route deals the least amount of damage, but it's still damage considering the FMC's innocence.
No matter what the outcome will be, the series will end in a tragedy, and I theorize that the FMC will lose since the title is: "Kusunoki's Flunking Her High School Glow-Up". Her relationship with the MC WILL flunk, She WON'T date the MC and if she does then it will FAIL. I theorize that the MC will choose Hebikawa since she is the most discussed about character in this community. The MC will be dumped since Hebikawa simply wanted to see Kusunoki crumble which she will.