ansatsu kyoushitsu
A 2012-2016 manga series by Matsui Yuusei, serialized in Shueisha's Weekly Shounen Jump, localized in English as Assassination Classroom.
The series follows the life and times of Class 3-E of Kunugigaoka Middle School, a notorious class full of misfits and academic underachievers, and their government-sanctioned attempts to assassinate their homeroom teacher Koro-Sensei, an octopus-like creature who moves at Mach 20, destroyed 70% of the Moon, and is threatening to do the same to Earth in one year, even as they struggle to come to terms with his uncanny talent and passion for teaching and counseling.