Yamibo - Darkness, the Hat, and the Travelers of the Books - S01

Hatsuki is a high school student who lives with her sister, Hatsumi, whom she secretly adores. On Hatsumi's sixteenth birthday, a strange green light envelops her, and she vanishes before Hatsuki's eyes. Desperate to find her, Hatsuki follows with the help of a peculiar creature that looks like a plump baby chick. She ends up in a place known as "The Great Library," where entire worlds are stored within books. Hatsumi isn’t there, so Hatsuki sets off on a journey through these book-bound worlds, determined to track down the sister she loves.