Satsuki Arashiyama

Satsuki Arashiyama is the younger sister of Jinpachi Arashiyama who is often seen with a wooden sword and she initially perceives Nanaka Kirisato as a hussy for making Jinpachi act all weird around her, so she tries to attack Nanaka, but Nanaka unintentionally dodges her attacks easily. After Nanaka "saves" her from a falling shard, she begs for her forgiveness and wants to be her disciple and she can address Nanaka as Oneesama (big sister). She then "trains" Jinpachi harder so he can be a worthy suitor for Nanaka.