Hatsuki is a high school student who resides with her sister, Hatsumi. She has a massive crush on her elder sister. On Hatsumi's 16th birthday, Hatsuki witnesses her vanishing in the presence of a green light. By obtaining the assistance of a chubby baby chick-like creature, Hatsuki chases after Hatsumi, landing them in a realm called "The Great Library." This place contains various worlds confined in books. Hatsumi isn't present, initiating Hatsuki's quest to find her true love by journeying through multiple books.