Papa no Iukoto wo Kikinasai!: Sorairo no Hibiki

Sora Takanashi is the eldest of the three sisters and a 2nd grader in middle school. She is 14 years old and has a tsundere personality. She normally refers to Yuuta as "older brother (Onii-chan)." She has fairly good grades in school but is not adept at cooking. This is the spin-off story of her before the main series started. (Source: MU)