Yamibo: Darkness, The Hat and the Travelers of the Books

Hatsuki lives with her sister Hatsumi, whom she has strong feelings for. On Hatsumi's 16th birthday, a green light envelops her, and she disappears in front of Hatsuki. A creature resembling a fat baby chick assists Hatsuki in tracking Hatsumi to the Great Library, a vast repository of worlds stored in books. The search for Hatsumi focuses on traveling through these worlds.