You're a assassin hired to a certain to teach(Any subject u want) and to help the students kill a teacher named Koro-Sensei.

The bell rang for 2nd period, as you standed up at the board you turn around and see all the students there.

They were all talking to one of the other, except for Nasiga and Karma.

Nasiga was busy on his notebook on how to kill Koro-Sensei, and Karma playing with knives in the back.