The school nurse and inventor of the G-On technology wielded by Yuuki, Sera, and Yayoi. She has the largest breasts of the entire female cast. Her true identity is that of Mako's younger sister (her real name is simply Sana). At some point in the past, she fell through a time warp and was aged several million years, causing her to go from the body of a 10-year old into a 20-something. She built Zero and created both the Maiden and Man Circuits. When she first came to Earth, her spaceship hit Ichiro and she transformed him into a cyborg, implanting the Man Circuit within him.

At Saint Hoshikawa School there is a secret group called the G-On Riders. Students with superior strength and ability are chosen to be in the group, which was formed to fight against alien attacks on the earth. However, many of the problems that the members face are ones amongst themselves, and the same is true for the invaders. And another student at the school, Ichiro, tries desperately to confess his love to Yuki, one of the Riders. <br><br>
(Source: Anime News Network)

An OVA episode included on the seventh volume of the VHS/DVD release in Japan.

Mio Sanada