Kouzuki, Mio

上月澪

Mio is a mute underclassman of Kōhei's who displays abundant expressions. Because she cannot speak, she relies on a sketchbook to conduct written conversations. She is a member of the theater club, serving as a junior to Yukimi Miyama. Although she performs non-speaking parts, she handles her role reliably. She is quite a dojikko, an anime stereotype for klutzy cute girls. In addition to the sketchbook she uses, she possesses an older one which she treasures greatly.
From Wikipedia.