It tells the story of a world where humanity has been destroyed by a catastrophic event known as the Great Collapse, and how a group of children who have been sent to a special school called the 'Horizon' to learn about the technologies that will help them survive in this new world. The story follows the main character, Hoshino, as he learns about the technologies and tries to find his place in this new world. The plot of Kyoukai Senjou no Horizon 3C revolves around the theme of technology evolution and its impact on society. The story takes place in a post-apocalyptic world where humanity has been devastated by the Great Collapse, a catastrophic event that wiped out most of human civilization. The few remaining survivors live in small communities, struggling to survive in a harsh environment. In this world, technology has become the key to survival, and the main characters are students at the Horizon, a special school that teaches them the skills they need to survive. The story follows the main character, Hoshino, as he learns about the technologies that will help him survive in this new world. He is a bright and curious student who quickly becomes fascinated with the potential of technology to change the world.

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