|Hometown||Meguro Ward, Tokyo|
|Manga Debut||Line 33; Children (Mentioned)|
Mio is a young girl who is, as noted by Mayu, very beautiful. Mio takes after her mother; she has long straight black hair worn into a ponytail with a straight hairline. She has light-colored eyes and long eyelashes.
Mio is presumed to live with her family in Tokyo. As Mayu claims, her father won't let Mio or his other daughters except for Mayu to rent an apartment, and he also told them to commute from home and come back home even when they married. As the youngest one, Mio is very fawned over in the family.
- The name Mio means "beautiful" (美) (mi) and "thread" (緒) (o).
- Mio's surname Sumimori means "housing, live/living, dwell/dwelling, reside, inhabit" (住) (sumi) and "forest" (森) (mori).