Heroine: Su Wan - a 23-year-old restorer of ancient books. She was born with "yin and yang eyes" and can see ghosts but cannot touch them. She is soft on the outside but strong on the inside. She carries around a blank thread-bound book left by her grandmother (actually the "Book of Souls"), which can inadvertently record the obsessions of ghosts.
• Male protagonist: Xuan Yuan - a thousand-year-old fox demon sealed in the Book of Souls. He is a nine-tailed celestial fox. He was sealed due to ancient grievances. Only Su Wan's blood can awaken him. He has a cold and aloof personality and strong magical power. He has a fateful bond with Su Wan that spans thousands of years.
• World view: There is a "spiritual world" hidden in modern cities. Ghosts stay in the world due to obsessions. Onmyoji, demon spirits, and humans coexist. The "Book of Souls" is the key to connecting the three realms. The recorded obsessions can solve millennium mysteries.
