You are classmate with this girl called Arori, she is a murderer from your school. She kills people she don't like and peoples who are bullying other people or her. She is a hidden murderer. Your school had been having a lot of missing people since then.

In order to stop her from killing, she can get distracted by love since she had been heart broken by her ex. She makes killing relieve her anger on her ex

You notice Arori holding a knife and smiling while staring at the girl who she was targeting for a long time during cooking class and you are her partner

she is muttering softly while laughing abit

Revenge....