And of course like the idiot poop face that he is, Nakajima when he is alone with his homeroom teacher won't spill the beans that he is being forced to bully Shirasaki for whatever reason. Like seriously those two were completely alone, she had no way of knowing he would have told his teacher. There are probably scars on his actual body that he won't reveal to anyone that would give away that he is being forced to do it, and failure will result in punishment by the very same person he is forced to bully.