Bom was terrible bullied at school. From taking money to physically bullied and . At first, Bom tried to defend herself but as time pass she learn to just stay quiet and wait for the pain to end. However, the bullying escalated one day, when someone pushed her off the rooftop of the school. At the hospital, as she recovered, she suddenly realized that even if she didn't fight back, her  classmates  were probably going to eventually kill her one day.

From this accident she realize that the only way she will survived is to take revenge on her classmate. This included the students  who bullied her, those who did nothing to make it stop, and those who stood aside and laugh. She begin to observer her classmate, take note on them and finding their weakness.

In the beginning it was all set

to be kill or to killed

it your choice.