In a very ordinary high school there is a strange class. A class of people who have been trained as killers in the process to accomplish a mission: to get rid of their new teacher, a lunatic octopus having decided to blow up the Earth. However, he seems immortal. He even takes pleasure in seeing others try to kill him, so how will they do to kill him before the Earth disappears? Why did this strange creature choose to come and teach? [mangasanctuary.com]