Ayuko has wavy chest-length dark purple hair that has bangs swept to the left and golden-brown eyes.
She wears school uniform at school, and white school team swimsuit on swimming.
- Ayuko's surname Kawase means "river, stream" (川) (kawa) and "swift current, rapids" (瀬) (se).
- Her name is revealed in Question 76.
- Ayuko, Uruka Takemoto and Chinami Umihara are come from Nanao Municipal Middle School, and participate in swimming team since middle school.