Ansatsu Kyoushitsu, Vol. 1 (Assassination Classroom #1), Yusei Matsui
Koro Sensei, a tentacle monster with the capability of reaching Mach 20 speed, is the teacher of class 3-E. He has already destroyed the moon and he promised that he will destroy the Earth if no one can kill him within a year. Ten billion yen is offered by the…