Ryoko was created by Washu, an immortal scientist. Washu used her own genetic material in creating Ryoko, effectively making them mother and daughter. Ryoko can fire beams of energy and manifest an energy sword.
She spend the first part of her life under the control of Kagato, an enemy of Washu. He used her a space pirate and Ryoko was widely considered a demon. A defeat severed her ties to Kagato and stranded her on Earth. On the plus side, Ryoko gained free will for the first time in her centuries-long existence. She fell in love with Tenchi, a human-alien hybrid, and ended up part of his household along with various other girls. An attempt by Kagato to reclaim control of her resulted in Ryoko reuniting with Washu. Who soon became both a new member of the household and another love interest for Tenchi. While much older than Ryoko, Washu maintains a more youthful appearance than her daughter.