(conditionally) Yukimi is a 2nd year high school student who plays the role of the ideal person at home and at school.

Spoiler

She is adopted and does not know who her real parents are or her true birthdate. Prior to living in her current household, she used to live in an orphanage, where she was abandoned as a child. She is one of the few people aware of Nagasawa being Raichi's father.