Kei Shirogane

Miyuki's younger sister. She calls Miyuki "onii" (big brother). She is in the 2nd year, Class B of middle school and serves as the student council treasurer. Born on August 1. Blood type B.

She has long hair and wears a lace headband. With a straightforward personality, she is popular among her classmates, regardless of gender. Due to their family's financial situation, she has developed a strong sense of economic awareness, much like her older brother. She delivers newspapers and uses her earnings to help with the household expenses. Her way of thinking and preferences are similar to her brother's, and she likes Kaguya.

Although she has entered a rebellious phase towards her brother, who also plays the role of a mother figure, and often badmouths him, she actually takes pride in him and feels happy when he is complimented. Despite being interested in Miyuki's love life, her rebellious phase prevents her from asking about it. She is good friends with Moeha, Chika's younger sister, and has long-known Chika herself, whom she calls "Chika-nee" (big sister Chika). She allows Kaguya to call her casually by her first name, "Kei."

Her mother left the family with just Kei after Kei passed kindergarten entrance exams while Miyuki failed. However, Kei and her mother later had a falling out (as Kei puts it, "rather than coming back, I ran away") and they now live with the Shirogane family.