The story of this anime is slow-building romance between the "reading princess" Dalian and their human protector Hugh Anthony Disward published chapter by chapter in the by Kadokawa Shoten.
Hugh Anthony is a guy who after the death of his grandfather, receives part of it a key that opens the Library Dantalian Mystique, a library of which few know its location and it is full of magic books, demonic energy and texts prohibited.
