Is it implied that Bocchi is cheating on Kita or something? Because the tone of the manga seems gloomy, but the story has a happy ending and a fairly mild conflict
Is she from the part of the manga that hasnt been adapted into the anime yet?
I could have sworn Sasaki appeared in the anime, but now you've got me doubting. But yes, she's basically a friend of Kita's who's also with Bocchi now; she's there to balance the group dynamic since Ryo and Nijika are at another school.