One of Harunas best friends at school.
Risa's partner and an avid cos-player, Mio is significant in the fact that she is the only named female in the entire series that never expresses an interest in Rito.
Mio, along with Risa, like to grope the other girls and take measurments. In fact, an entire anime episode is dedicated to that. The kicker of that is when everyone else has gone, Lala innocently reminds the girls that only Mio and Risa weren't measured.