The Path of the Nightmare is a fantasy novel by Boris Romanovsky, the fourth book in the “Niel” cycle, genre: action fantasy, isekai.
Days passed, months passed, and the nine-colored door continued to hang high in the sky. Ordinary people had long stopped paying attention to it; it seemed to have dropped out of their field of view, becoming something ordinary and familiar. Not many knew what the appearance of this sign foretold. An invasion. The demonic race—second on the list of Rённе—officially entered this world.