Assassination Classroom The movie : 365 Days

It is 2015. The Moon has been destroyed by a tentacled alien creature which threats to attack the earth. The only solution to save the planet the alien says, is to let it teach the worst class of the Kunugigaoka secondary school. In 365 days, if the students have not succeeded in killing their sensei, the earth will explode. But is it possible for some teenagers to succeed in assassinating an alien that can, not only reach a speed of Mach 20 but also appears to be the best and the most lovable teacher they’ve ever had ?