Mio Natsume (夏目 美緒 Natsume Mio?) is ToQ 3gou (トッキュウ３号 Tokkyū San-gō?, ToQ #3), the Yellow Ranger of the ToQgers.
Mio was one of the friends, as well as classmates of Right Suzuki, Haru Tokashiki, Hikari Nonomura, and Kagura Izumi. She also had an imagination friend, Mikey, which only Hikari is aware of. When Emperor of Darkness Z's darkness as well as the Shadow Line invaded Subarugahama, their home, Mio and her friends were spirited by the Rainbow Line light while Right was consumed by the darkness. Nonetheless, she and three other friends were turned into adults by Rainbow Line President's Imagination and hired as ToQgers, rescuing cities that were invaded by the Shadow Line.
One day, Mio and her friends managed to reunite with Right, their old friend when he was mistakenly kidnapped in one of Bag Shadow's Kuliner. After Right was appointed as ToQ 1gou, he accidentally unlocked one of their functions, the Transfer Changes and managed to defeat Bag Shadow. Ever since then, she and her teammates resorted to free towns that were invaded by the Shadow Line while searching for their old hometown. They also receive an aid from Akira Nijino, whom formerly a former Shadow Line worker Zaram that gained the mantle of ToQ 6Gou.
In one incident, Hammer Shadow materializes Mikey from her and tried to dispose him to bring Mio into despair. However, thanks to Mikey's mischievous nature, it barely escaped before protecting Mio from Hammer Shadow. Instead of falling into despair, Mio rebounded and managed to attack Hammer Shadow before the latter was saved by General Schwarz.
During the Christmas event, they managed to find their hometown, Subarugahama but were surprised when discovering that the town is now the foundation of Castle Terminal.
After the Castle Terminal was relocated out of Subarugahama with the town was purified by Gritta's assistance, Mio and her friends were tricked by Right into giving their Rainbow Passes to prevent their interference in Right and Akira's raid into Castle Terminal, as well as to ensure their safety by turning them into children and left them in their normal lives without Right's existence. Unknown to Right, Akira and Wagonhad planned to make them remember their older selves with previous photos of them and Right placed on their tree base as a safety precaution and backup plans. Thanks to the photos, Mio and the others reuse it as their new Rainbow Passes and managed to rescue Right from despair in the darkness. Along with the ToQgers, they defeated the remaining Shadow Line armies, and seemingly defeated Z before Gritta spirited him with a Kuliner. The five core ToQgers were seemingly trapped in their adult forms but their families were able to remember them due to their Imaginations and finally returned to their child forms. Akira and the other Rainbow Line departs, while the children continue their regular lives.