Classmate with Tamaryu and Ran, and whose teacher is Shizuki in the new Youkai school that opens up, she appears in the school-related strips. She appears more often as the school becomes a more prominent feature of the series.
"Catherine" is her nickname based upon the fact that she is the mixed-blood daughter of a canine youkai and a fire bird youkai--the kanji for "fire" "bird" "dog" can be pronounced like "Ka-Tori-Inu", or how a Japanese person would say "Catherine". Her actual name is Inukai Suzume.
As a fire-bird-dog, she has an unusual body with large wing-arms, dog-ears, a tail, and apparently a weakness against water.
