I read a manga about a female transfer student that befriends the most popular girl in class, a site on her phone appears and it asks which student would the person most like to die. Thinking that it was a practical joke, she votes for her "best friend", the next day a humiliating video is posted in class.
Just before she can confront her friend, the girl dies from a hit and run accident. Traumatized, she believes that the app can kill anyone of them and the odds can be against her favor. She tries to find the culprit and learns about the truth, before her transfer there was a female teacher who had cursed their class before she committed suicide from her students mistreatment.