Kosuzu Motoori

Kusuzu is the human girl who works at the book rental store attached to her house, Suzunaan. She lives with her parents and is friends with Reimu, Marisa, Aya, Akyuu, and Mamizou

Kosuzu is a girl with red eyes, ginger hair and twintails adorned with bells. She wears a checkered kimono and apron with Kosuzu and 鈴奈庵 (Suzunaan) written on the front. She uses glasses to read. When she goes outdoors she wears a coat.

Kosuzu has a sweet personality, considerate and optimistic, polite and cheerful with her customers and her friends, and enjoys telling stories to village children. However, she is very confident in herself and her abilities, which frequently gets her into trouble. She thinks she knows better than most other people, originally distrusting Reimu and often taking matters into her own hands, with disastrous consequences (as when she tried to summon a smoke youkai to deal with a word worm. She's highly curious, and often dangerously so, being unafraid to read and make use of the Demon books she owns, even after learning that they contain the power of youkai, and goes to many different measures to acquire information.
Despite this confidence, she can be quite cowardly as well. She's also prone to fainting when startled, whether it be in a dangerous situation or even if it's actually something benign. she also has a fear of snakes
Originally frightened of youkai, once she was told about the true relationship between humans and youkai, she reacted with excitement and expresses interest in one day participating in danmaku duels.

Family - she has a family that she lives with and even talks to them while she's working

Mamizou Futatsuiwa - A regular patron of the store in her human disguise, Mamizou Futatsuiwa speaks to Kosuzu in a friendly manner and offers her advice on supernatural matters. She looks up to Mamizou and usually trusts her more than others

Hieda no Akyuu - Kosuzu's closest friend, and the two often meet to discuss books and strange happenings. Kosuzu is noticeably more casual and outspoken around Akyuu than while speaking to her elders like Reimu and Marisa. However, it seems Akyuu has a preachy side, which annoys Kosuzu

Reimu Hakurei - Kosuzu seems to know and respect Reimu very well, speaking to her in a friendly and polite manner.

Marisa Kirisame - As a frequent customer of Suzunaan's and a fellow collector, the two are on friendly terms.

Aya Shameimaru - Kosuzu and Aya have become business partners in the selling of the Bunbunmaru Newspaper for the Human Village (which Reimu also helps with to make sure no slanderous things are in the papers)

Yukari Yakumo - Although not knowing too well, Kosuzu does find out more about the relationship between youkai and humans because of her. She's also the reason Kosuzu took the scrool that turned her into a youkai temporarily.

she refers to most of these people in a very polite manner as "Miss" or "Mr" (I.E. Miss Reimu, or Miss Mamizou)

Suzunaan is a traditional Japanese style book renter located somewhere in the Human Village. Although it is a book renter, they also sell books, and even provide a small book printing service. The Gensokyo Chronicle (Perfect Memento in Strict Sense) written by Hieda no Akyuu was also printed and bound here. Most of the books they deal in are the books that drifted into Gensokyo from the outside world, which they call "foreign books" (外来本 gairai bon). Kosuzu has been also secretly using some income of the store to gather a collection of rare demon books, and rents out at high price. Suzunaan also sells the Bunbunmaru newspaper (written by Aya Shameimaru and checked by Reimu Hakurei)
Kosuzu Motoori is a worker at Suzunaan. Hieda no Akyuu also appears to use it as a tool for her own research.
Because Suzunaan is like an extension to their home, Kosuzu's parents also tend to work and be in that area to check on and help their daughter.