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

Hazuki is a high-school student living with Hatsumi, and the two are so close they are like sisters. On Hatsumi s 16th birthday, she is suddenly surrounded by a green light and disappears right in front of Hazuki! Hazuki manages to follow Hatsumi with the help of a yellow parakeet named Ken, and ends up in a place called The Great Library,
full of different worlds stored in books. But Hatsumi isn t there, and so the search begins…

Based on an adult visual novel from the early 2000s, Yami to Boushi to Hon no Tabibito.