Living with her beloved sister Hatsumi, high school student Hatsuki finds herself on a quest to find her missing sibling. Aided by a chubby chick-like creature, Hatsuki ventures into the mystical realm of 'The Great Library', a repository of diverse worlds bound within books. As she embarks on a journey through various realms, the search for her cherished sister and true love unfolds across the pages of different stories.