The abyss, an invisible anti-world will, causes the imaginary number space to erode the real number space. All the eroded parts will first be unable to maintain their original appearance, and then they will not be able to maintain their consciousness. Together with their material composition and spiritual composition, they will become energy particles floating in the imaginary number space, and will be swallowed up as food by the concrete beasts living in the imaginary number space. Even if there are humans who are lucky enough to retain their own appearance and consciousness, they will eventually be eroded by the abyss and become the agents of the anti-world will - the Black Knights. They have the appearance of humans, but have lost the emotions of being human. They are given powerful power by the abyss to destroy the world of real numbers, and their appearance will bring about the erosion of imaginary numbers.