Space Pirate Ryoko
Of all the characters in the Tenchi Muyo series Ryoko is my favorite. She causes so much trouble for poor Tenchi. Ryoko draws her power from three stones one around her neck and one on each wrist. Ryoko is a demon who until the first episode Ryoko Resurrected was imprisoned in a cave just outside the Masaki Shrine. She was released by Tenchi after his grandfather tricked him into going into the cave. You'd think that she'd be more thankful considering he released her and restored her beauty. But then again this Ryoko after all.
Ryoko is the protagonist in this series. She is an Oni, an ancient Japanese devil. She was created by Washu my using a simple life form called Mass and from one of Washu's egg cells. Because of this Washu considers Ryoko as more of a daughter rather than an invention. When Zero copied Ryoko she absorbed some of her memories. After Zero allowed her emotions to surface, Washu combined Zero and Ryoko. The result was Ryoko with more obvious emotions. Ryoko's chief rival for the affections of Tenchi is Princess Ayeka. Ayeka is the crowned princess of Jurai and has the mannerisms and powers that come with her position. While Ryoko is outgoing and brash, Ayeka is more withdrawn and proper.
Little is known about Ryoko's past before her battle with Yosho. Before and during the battle Ryoko was under the control of Kagato. He took over her after imprisoning Washu and taking Soja. Kagato used her to lead the only successful attack on Jurai. The power in her gems is so similar to that of Jurai's trees that she managed to slip by the Jurain border. During her attack on Jurai she shot down a ship that crashed into a building. Sasami was in that building and fell to her death. Kagato sent Ryoko there to find Tsunami and capture her. She could not find Tsunami and was forced to retreat. Yosho pursued her and eventually caught her on Earth.
After that she spent 700 years in the cave near the Masaki shrine. While trapped in the shine she created a pseudo-gem which she used to fight Tenchi with. That gem was incomplete when Tenchi found her. Tenchi later destroyed it during their fight. While Tenchi was growing up she watched over him and fell in love with him when he got older.