Mizuki Akiyanagi is the younger sister of Takateru.
Mizuki is a girl with blonde hair, slim body and sleepy appearance.
Mizuki is a cheerful, friendly and innocent girl. She has her great affection for her brother and hates people that upset, this is clearly seen in his attitude towards Saki.
He's her older brother. She's possessive of him especially when it involves Saki Kirishima.
Yumeji and Mizuki are friends from the past, presumably presented by his older brother Takateru. Mizuki seems to have fantasies where Yumeji and his brother are in homosexual situations.