Admittedly, this show is a strange one…it follows a class of students who are forced to assassinate a tentacled creature who is threatening to destroy the world, dubbed “Koro Sensei”. It’s a bit different because it really throws everything on the table at the beginning of the series, so there isn’t really much to speculate. In this episode, it’s revealed that Koro is born and raised on Earth, so he’s very likely a government experience. This is reinforced by the scene at the end of the episode where a dying scientist asks him to become a teacher.
So, he’s probably a government experiment gone awry that is only using the threat of destroying the world as an excuse to fulfill that dying request (he might even be in danger of dying naturally in a year). So the rest of the series becomes mostly character development of the class and stuff…with comedy? I guess that’s the only way I can sell it. Final remarks: the opening song was boring to me, but the ending song sounded like it had potential.