The topic of this story is responsibility.
Sarah feels the social responsibility to stand up for a girl Lara who she feels is in danger or threatened. She feels that, as a witness to the bullying, she needs to do something.
Though some may think it is friendship, it isn't likely because Sarah barely knows Lara personally.
Though there are hints of violence that could happen in the story, it is not the main focus. The same goes for music.