Shiroi Bara no Otome

Yoshiko Hamaguchi, a third-year high school student at a missionary school for girls, spends her days bored in an all-girls school filled with gossip and boring camaraderie. One day, she meets Tsukiko Takamiya, the queen of the school, in the old auditorium, which is now closed. The next day, Tsukiko asks to be friends, but there's a trick on her mind...

(Source: Shogakukan, translated)