As Nariyuki Yuiga's younger sister, Mizuki shares a strong physical resemblance to him, having the same facial features as his (though hers are slightly more feminine). Mizuki's black hair is styled in a way that frames her face at the same time it is tied in a ponytail. Her breasts are much larger than Fumino Furuhashi.
During the week, Mizuki mostly wears a middle school uniform, while at home she wears an apron with printed words.
Mizuki has a serious brother complex who tends to show a slight yandere personality when Nariyuki is around other women such as Fumino.
She mostly prepares housework for Nariyuki Yuiga at home.
- The name Mizuki means "water" (水) (mizu) and "hope" (希) (ki).
- Mizuki prepares lunch and dinner for family members.
- Mizuki is good at housework.
- Mizuki's aprons are printed in different English messages.
- Mizuki's school uniform is same as Uruka Takemoto at middle school, which is later revealed to be a student of Nanao Municipal Middle School.
- Mizuki knows Haruma Kobayashi in childhood, and later Kanade Oomori.
- Mizuki begins swimming when she met Uruka in childhood, and participates in swimming team where she admires Uruka.
- She enrolled Ichinose Academy by principal's recommendation on sports in final chapters.