如月 真綾

Maaya is the older sister of Yuu. She attends the same school as her brother and is his senpai. She is very famous and loved by all in the academy.

She loves Yuu so much and often asks him to massage her shoulders after getting out of the bath. She shows almost no embarrassment towards him, even complaining to him that her breasts keep on getting bigger. 

One day when she got home from her club activities early, Maaya heard Yuu calling her name in his room and she decided to go see if he was okay, only to find him in a very embarrassing situation. Her reaction, however, is surprising: she asks Yuu if he's calling the onee-san in his manga or her.

And this event marked the beginning of their story.