Mio is a second year student who hangs around with Omi. Due to her short stature, she is often mistaken for a grade school student and has even received multiple confessions from grade school students. She is in fact half frog spirit and can heal quickly. While she did not have a name originally, Omi named her from a combination of his own given name and his home town's name. She is on good terms with Omi.
Source: Wikipedia.