Mio appears in "Needless+: Saint Lily Gakuen no Himitsu" within the "Needless" universe. As a member of Simeon's Killer Girls Squad, she presents a youthful appearance and happy-go-lucky demeanor. She has short pink hair often adorned with a yellow bow and typically wears her squad uniform. Her physical measurements are height 147 cm, bust 71 cm, waist 56 cm, and hips 77 cm.

Mio wields the Fragment ability "Power," granting immense physical strength. This allows her to effortlessly wield heavy objects, including her Orichalum stuffed bear (which she mistakenly calls a rabbit). Her fighting style blends street fighting and wrestling, featuring attacks named like "Mio-chan's Hip Attack."

Within the main series narrative overlapping the OVA setting, Mio initially pursues Adam Blade under Simeon's orders but later allies with Cruz Schild after separation from her squad. She develops a close bond with Cruz, using his name instead of the derogatory "Yamada." Her affection for Blade leads her to call him "Onii-chan" and travel with Cruz to reunite with him. She designed and commissioned her Orichalum bear from robotic toymaker Zepetto; it features a concealed, unsettling face beneath its ears.

Mio participates in key battles against opponents like Nanami, Hatfield, and Ishiyama. She sustains severe injuries against Hatfield but recovers. Later, Ishiyama overpowers her and throws her through a wall, though her survival is implied by the scene's comedic tone. Her story arc includes brief separation from Cruz during the St. Rose Academy incident and subsequent reunion.

Within the "Saint Lily Gakuen no Himitsu" OVA episodes, Mio's role and traits align with her established portrayal from the main series.