Kai gaslighted Bocchi. She told Bocchi that she will end their friendship because Bocchi should befriend all of her classmates in her new school because Kai and Bocchi are gonna be in separate schools and if Bocchi succesfully did that Kai will go back to Bocchi and resume their friendship. Kai is aware of Bocchi's emotional and psychological state that's why she did that.
On the positive side of my review, I only enjoyed the whole series was because of Aru and Nako. I love how Nako teases Aru about her being the unfortunate girl and it's freaking hilarious how Aru responds to Nako's tease!
Personally, I won't watch this anime again just because of Bocchi. Hated her personality from start to finish of this anime.
