In the land of Lu—a country reviled for its ominous black color—lives Princess Rinka, a young woman so in love with books that she's known as the "Book Youkai." After her engagement is annulled, several years pass until, by a twist of fate, she is sent to the imperial harem of the Celestial Emperor. Faced with a future full of obstacles, Rinka must navigate the treacherous life of the inner palace… armed with nothing but her vast book knowledge!