Ritsu

"She" is a killing machine brought from Norway with the intent to kill Koro-sensei. At first, she acts like a robot, calculating all of her moves and even manages to hit Koro once. After her classmates start to complain about her assassination style (which consist of non-stop barrage of shots), Koro completely changes her, imputing a bigger screen that covers all of her body, changing her facial expression to a livelier one and the way she talks.