Mio Osakabe, a timid second-year high school student, possesses a petite frame often mistaken for a grade schooler’s. Her appearance features blunt bangs and neck-length black hair framing brown eyes, paired with a school uniform adorned with knee-high socks and a bow. Beneath her youthful exterior lies her hybrid nature as a half-frog spirit, granting her rapid healing abilities.

Once nameless, she was christened "Mio Osakabe" by Omi Kiriyama—a sickle weasel spirit and peer—who wove his name and hometown into hers. She is frequently seen alongside Omi, their close bond sparking flustered reactions from her when mentioned. Though her unspoken feelings for him linger beneath her reserved demeanor, they remain concealed by her shyness.

Her ties to Omi imply a history shaped by the supernatural currents within their school. While engaging with others, she assumes a supportive role in Omi’s endeavors, her gentle nature and steadfast loyalty defining her presence in his story.