Naga-ame (a Touhou LW original) refers to rainfall that lasts for a long time. When it rains for days on end, it is the perfect time to read books, which makes this temperament a good fit for the face of the Suzunaan book rental shop. Kosuzu is endowed with Wood Phase, as she works in a bookstore, and Star Essence, with her highly curious personality. The strong and kind Wood Phase resists Water Phase, because water nourishes wood, but it is weak to Metal Phase, because metal carves wood. The diverse and uncooperative Star Essence resists the cooperative and indecisive Moon Essence, but it is weak to the charming and arrogant Sun Essence.

Kosuzu Motoori is capable of reading any language, even languages used by youkai, as long as the text is made up of symbols that can be perceived as letters or characters. Consequently she can read any and all demon books. There seems to be no limit to the type or amount of languages that she can read. She has been seen reading a demon book written in the ancient tengu language and Suzunaan deals with handwritten copies of magic books from the outside. However, even if the symbols on a text are in fact letters, Kosuzu can only read it if she herself recognises that these symbols are a form of letters or characters. Her ability appears to still be evolving as she has gained the capability to sense the aura of books. This may or may not be related to Kosuzu's ability, but in the outside world there is a peculiar theory that recorded information could be transformed into energy. If this is true, it may mean that every book is imbued with some sort of magic...