Mio is a fifteen year-old bookworm. She continuously reads about things that came to her interest and eventually discovered ninjas. After that, she couldn't get enough of them. She started practicing the basics in her room then on the roof of her building (due to many broken head boards). She would sometimes see figures jumping the rooftops and dismiss them as her imagination. That is, until the shadows got too close to her practice area then she went after them. She discovered the Ninja Turtles.

She tried looking for them again on ground level and was caught by the Kraang, who saw her follow the turtles. After the Kraang took her, they questioned her and failed to get any information. So they put her in a tank with fluid to alter her brain chemistry so she would answer them. This caused one eye to become gold and the other to become a lighter blue (originally had sapphire blue eyes).