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

Hatsuki is a high school student who lives with her sister, Hatsumi, and secretly harbors strong feelings for her. 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 chubby baby chick. She ends up in a place known as "The Great Library," where countless worlds exist within books. Hatsumi isn't there, so Hatsuki sets off on a journey through these book-bound worlds in search of the sister she loves.