She is an "elite girls' high school swimming club member." She is in class 2-D at Yosento Girls High School, a high-class school. She is ignorant of the ways of the world. She has always attended a girls' school, so she is jealous of those who go to co-ed schools.
- The name Miu means "water" (水) (mi) and "feather" (羽) (u).
- Miu's surname Hiyama means "Cypress" (桧) (hi) and "mountain, hill" (山) (yama).