Saya was born in England to a family involved in trade between England and Japan. After refusing to comply with a gang led by Oboro, her family was killed by an extermination unit, but she was spared and raised by one of the assassins. Trained in assassination, Saya harbors a deep hatred for Oboro's Razor Trio and the Bafuku government, whom she blames for her parents' murder. She has joined Jushiro's Atom Rebels to overthrow both the Bafuku and the Razor Trio in Riten Kyo.