Mio Sanada serves as the school nurse at Saint Hoshikawa School and is the inventor of the G-On technology used by Yuuki Kurama, Sera Arashiyama, and Yayoi Hoshikawa to fight alien invaders. Her true identity is Sana, the younger sister of Mako, the leader of the alien group known as the Roribeders. In her past, she fell through a time warp that aged her from a ten-year-old child into a woman in her twenties over the course of several million years. Upon first arriving on Earth, her spaceship accidentally struck Ichiro Hongo, and she transformed him into a cyborg by implanting the Man Circuit within him. She also created the android Zero and developed both the Maiden Circuit and the Man Circuit, key components of the series' technology. Throughout the story, Mio acts as a behind-the-scenes supporter, providing the G-On Riders with their equipment and guidance. Her motivations are rooted in protecting Earth from the ongoing alien attacks. Her relationship with her sister Mako is complicated by their reversed ages due to the time warp, yet she remains involved in the conflict that involves Mako and the alien forces. As the creator of Zero and the circuits, she plays a crucial role in enabling the protagonists' powers and in Ichiro's transformation into Cosmo Banchou. While her personality is not extensively explored, she is depicted as a calm and competent figure who takes charge of scientific development. Notably, she is the character with the most prominent physical attributes among the female cast. Her abilities are centered on advanced technological invention and engineering, rather than direct combat. Mio's development is limited, as she consistently fulfills the role of the inventor and caretaker without undergoing a significant personal arc; she remains a static but essential supporting presence throughout the series.