Ansatsu Kyoushitsu

Synopsis

Karma Akabane, a somewhat sadistic student who transfers into Class 3-E following a suspension, manages to inflict some damage to Koro-sensei using some clever pranks. As Karma continues his assassination pranks, however, Koro-sensei starts to avoid them and do some pranks of his own. Determined to take Koro-sensei down no matter what, Karma jumps off a cliff with a gun in hand, hoping to force Koro-sensei into either getting himself killed trying to save him or destroying his pride as a teacher. As he falls, Karma reflects on his own hatred of teachers, which occurred when a teacher he had trusted turned against him when he got in a fight protecting a Class E student, caring more about the school's image than him. However, Koro-sensei manages to save Karma using his tentacles, which leads Karma to come to accept him as a teacher.

(Source: Wikipedia)