Mitsuki Nase

Nase Mitsuki is the sadistic second daughter of the famous underworlder Nase household. She is with Akihito in order to observe him, but she is in fact very worried about him. She is good enough friends with Akihito to be able to speak frankly with him, and is the president of the school's literature club as a second-year student.

(Source: Anime News Network)