Kosuzu Motoori is a carefree human girl living at Human village and working at the Suzunaan book renter. She has just recently gained the ability to dechipher all books by just touching them. She uses this ability for reading youkai books, not caring much about their dangerous nature. Kosuzu is shown to be acquaintances with Reimu Hakurei, Marisa Kirisame and Hieda no Akyuu.
Kosuzu Motoori is the main character of Touhou Suzunaan - Forbidden Scrollery.
Youkai books, or in other words youma or demon books, are books written by youkai. They can be old classics simply written by youkai, books written for humans by youkai, or grimoires used by magicians. Most often though, they are books recording a youkai's existence. For a youkai which has its existence denied, the only hope to escape the fate of disappearing entirely from the cycle of reincarnation is to record its own existence and seal oneself in a book, waiting for a chance to be revived again. Reading youkai books with a youkai's existence recorded in it can be dangerous, as there is a chance the youkai might be revived.
Most of the time youkai books are unreadable by humans, as they are written in unknown characters. This is why youkai books are very rare in Human village. Kosuzu Motoori however, who has the ability to dechipher any book, enjoys reading and collecting them, stating that she no longer has interest in normal books. She prides herself as the No.1 collector of youkai books in Gensokyo.
Suzunaan Book Renter:
Kosuzu Mootori is a worker in this traditional Japanese style book renter. Despite being a book renter, it also seems they sell and print books. It is stated that The Gensokyo chronicle (Perfect Memento in Strict Sense) written by Hieda no Akyuu was also printed here.
Suzunaan mostly deals books from the outside world, but recently Kosuzu has started collecting youkai books for the store in secret.