I'm a librarian who loves anime, manga, and reading a wide variety of genres.
An alien later named Koro Sensei has destroyed a huge chunk of the moon and plans to destroy the Earth, but first he's going to be the best teacher Class 3-E has ever seen. If any of his students can kill him prior to graduation, they'll not only have saved the Earth, they'll also be awarded 10 billion yen. Their weapons are special rubber bullets and knives that are relatively harmless to human beings but fatal to Koro Sensei...if they can manage to touch him. All of their efforts fail, but Koro Sensei finds ways to motivate them and, weirdly, lift their spirits. For example, Sugino learns to pitch better, Okuda learns the value of good (and appropriately used) communication skills, and violent Karma finds in Koro Sensei a teacher who will truly stand by him.
This series is like a parody of those heart-warming movies from the '80s and '90s about teachers who find a way to connect with their classrooms of supposedly hopeless delinquents. Even as Koro Sensei evades his students' assassination attempts, he finds ways to help them feel supported, learn their strengths, and realize why academic subjects they dislike are still worth learning.
So far, I like this, although the moon thing bugs me. If that much of the moon were destroyed, the Earth would already be doomed. I had to do my best to just accept it and move on. I enjoyed the humor, I loved serious-looking Karasuma as their PE teacher (concentrating more on assassination techniques rather than traditional PE activities), and Koro Sensei's work with his students was oddly touching. I'm looking forward to eventually finding out Koro Sensei's motivations. Here's hoping it doesn't take too long. At this point, all readers know is that he made a promise to what appeared to be a dying human woman.
(Original review posted on A Library Girl's Familiar Diversions.)