Manga Like Koroshi Korosare Sankaku Kankei ni Watashi ga Ima kara Hairun desu ka?

Kohaku was a loner in junior high school, and she dreams of a more fulfilling social life in high school. However, on her first day of school, she falls down the stairs and ends up hospitalized for a month! This means that everyone else has already made friends and formed groups at school... In order to avoid being left all alone, she summons up the courage to talk to the only odd-numbered clique in her class. But it turns out that they are at the top of the school social caste, and they are caught up in a blood-splattered yuri love triangle...!? A suspenseful high school comedy about trying to fit in! (Source: ComicWalker, translated)