Кадзуки Косуда

Такаси's older sister is 4 years older than him. She attends university. From a young age, she has had a masculine personality, which has sometimes made her the object of affection for girls. In particular, she was Miya's first love (who thought Kazuki was a boy at the time); even now, she still receives Valentine's gifts from girls. While she often teases Takashi and his love life, she genuinely cares for him as an older sister.