The adorable creature Ryo-ohki is actually the creation of the scientist Washu who also resides at the Masaki home. Ryo-ohki was created from an amorphous aquatic lifeform known as the "Mass". Ryouko was also made from the same "Mass", and both Ryouko and Ryo-ohki share a mind link between each other.
Ryo-ohki was created about the same time Ryouko was, so Ryo-ohki shares the same age of about 2000 years. However, she only has had her cabbit (cross between a cat and a rabbit) form for about a year. Ryo-ohki acquired this form after her original form was destroyed in a battle with Aeka's Ryu-oh. Ryo-ohki still possesses the ability to transform into her spaceship form due to the crystal in her forehead. There is a poetic justice in this since the original Ryu-oh also ends up being destroyed, but later there is sort of relationship between Ryo-ohki and the tree Ryu-oh to the point where they can combine to form a super spaceship with Ryo-ohki's firepower combined with Ryu-oh's ability to create the Light Hawk Wings as all high-generation Juraian ships can. Later, she also acquires a female humanoid form when she assimilated once again with the "Mass" in order to protect Tenchi who was threatened by the out-of-control "Mass".
Ryo-ohki's history is closely linked to that of Ryouko. Ryo-ohki served as Ryouko's spaceship in various raids on planets when both of them were originally under the control of Kagato after Kagato betrayed Washu. Ryo-ohki assisted Ryouko in capturing artifacts for Kagato and destroying many worlds in the process. Then, about 700 years from the present, they both attacked Jurai in an attempt to capture the sword Tenchiken as well as Tsunami, the most powerful Juraian tree who was also a deity. However, they failed to capture either, and they were pursued to Earth by the First Crown Prince of Jurai, Yousho, who severely damaged Ryo-ohki with his ship Funaho and went on to defeat Ryouko and imprison her in a nearby cave. Ryouko was set free from the cave by Tenchi, the grandson of Yousho, 700 years later, and Ryouko was once again summoned, this time to battle Aeka, the First Crown Princess of Jurai and Yousho's half-sister. The ship Ryo-ohki was destroyed in this fight, but the ship was able to reproduce itself in the form Ryo-ohki takes most of the time...that of an adorable cabbit.
Ryo-ohki shares Ryouko's ability to phase through solid objects. Ryo-ohki is also mind-linked with Ryouko, meaning that whatever Ryo-ohki sees or hears, Ryouko can gain access to. Ryo-ohki also is able to fire a beam from the crystal on her forehead, but only for defensive purposes. When in cabbit form, Ryo-ohki can lift objects or people that are many times heavier than she is by levitating them, although using this ability is very taxing on Ryo-ohki. Of course, Ryo-ohki also possesses the ability to change into either one of three forms, although it is difficult for Ryo-ohki to maintain her humanoid form for very long. The form Ryo-ohki prefers is that of a cabbit.
Ryo-ohki gets along really well with everyone. Even Aeka, who does not get along with Ryouko most of the time, likes Ryo-ohki especially after Ryo-ohki kept her company when she thought she had lost everything after the loss of Ryu-oh. Ryo-ohki especially gets along really well with Sasami, Aeka's little sister. The two are best friends, and at times they seem almost inseparable. Ryo-ohki goes out of her way to try to please everyone, whether it's delivering mail for Aeka, fishing for Ryouko, or helping Tenchi harvest carrots. Ryo-ohki seems obsessed with carrots, and there are few things that Ryo-ohki would not do just to be able to have a carrot. Ryo-ohki is a great addition to the Tenchi family, and she just goes to show that sometimes powerful friends are found in the cutest of packages.