The bottom class of the prestigious Kujigaoka Junior High School, Class 3-E, welcomes a strange teacher (voiced by Kazuya Ninomiya) in the new school year. This teacher has a round yellow head and slimy and disgusting tentacles. It turns out that he is the culprit who blew up the moon into a crescent not long ago. The elite of the Japanese Ministry of Defense Special Forces, Kazuomi Karasuma (played by Kippei Shiina), introduced the monster to the students. He has an ultra-fast speed of Mach 20, and ordinary human weapons have no effect on him. In order to prevent the monster's conspiracy to destroy the earth in a year, humans must find ways to get rid of him. The monster volunteered to be the head teacher of Class 3-E, so the powerless students took on the task of assassinating the monster. Since then, the students have received strict training from Karasuma, and powerful opponents such as the killer Biki (played by Chiying), the intelligent robot Autonomous Thinking Fixed Turret (played by Hashimoto Kanna), the transfer student Horibe Keinari (played by Kato Seishiro) and the instructor Takaoka Akira (played by Takashima Masanobu) have also come to this assassination classroom one after another. The funny "Kuro-sensei" will face endless assassinations... This film is adapted from the super popular manga by Matsui Yusei.