Koro-sensei is the main protagonist of Assassination Classroom and teaches class 3-E at Kunugigaoka Junior High School. He's best known for being virtually indestructible—his name literally means "unkillable teacher," a play on the Japanese word for "cannot be killed" (korosenai) combined with sensei.
Before becoming a teacher, Koro-sensei carved out a massive chunk of the moon, turning it into a permanent crescent. He's got a pretty wild plan: teach class 3-E for one school year, then destroy the Earth. The catch is that the government has tasked his students with assassinating him before that happens, which sets up the whole premise of the series.
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