Ritsu

律, Fixed Autonomously Thinking Artillery
An artificial intelligence developed by Norway and sent to Class 3E as a transfer student to dispose of Korosensei able to learn his movement patterns and perfect her shooting skills in order to eventually kill him. After receiving a few modifications from Korosensei she develops a conscience and becomes friends with the rest of class 3E who give her her shortened nickname. Thanks to her processing power she frequently helps with Intel gathering and communications and usually interacts with others via a smartphone application developed by her classmates. She is portrayed by Kanna Hashimoto in the live action movie. Source: Wikipedia
122