Touhou Suzunaan: Forbidden Scrollery. is a Touhou official comic published by Kadokawa. It introduces the human book renter and collector Kosuzu Motoori as the main character, with the story centered around her mysterious ability to decipher any book no matter the language or script, and her assortment of various rare and dangerous demon books.
Marisa Kirisame runs into Hieda no Akyuu on her way through the Human Village, and notices that she's carrying a strange book—a youma book, said to be indecipherable. Afterwards she makes her way to the Hakurei Shrine to ask Reimu Hakurei about them, but she doesn't know much on the subject. Marisa explains their dark and mysterious nature, and the two decide to take a visit to Suzunaan to talk to Kosuzu Motoori about it. She reveals her collection of demon books, as well as her recently-awakened powers that allow her to decipher any sort of script. Reimu worries that it might be dangerous, but Kosuzu is not very concerned.
(Source: Touhou Wikia, MU)