Hajimete no Satsujin

"We are murderers, you know." Mayu is your average high school girl who goes to a prestigious school for young ladies. Her school life there feels fulfilling thanks to her close friends, Oto and Yuu. However, one day, Mayu and Yuu witnessed Oto pushing their class teacher who then fell and lost consciousness. Oto tries to explain that the latter has only passed out but...!? (Source: Shueisha, translated)