Ryo-Ohki is a "Cabbit" that's a cross between a cat (meowing) and a rabbit (a distinct love for carrots). Ryo-Ohki transforms into a Ryoko's spaceship. Ryo-Ohki spends most of her time playing with Sasami. Ryo-Ohki was created by Washu. She is also one of the most popular characters in the series.
Ryo-Ohki transforms into the space pirate Ryoko's spaceship, which can be seen below. While Ryoko was being controlled by Kagato in the OAV, Ryoko and Ryo-Ohki lead the only successful attack planet Jurai. Ryo-Ohki's power comes from Ryoko's gems which is the same as the power that comes from the trees of Jurai. Since this power is the same she was able to sneak past the defense systems that prevent non Jurain ships from entering Jurai space without permission. During this battle Sasami was killed and after which Yosho went off to fight Ryoko on planet Earth.
Ryo-Ohki has died many times. But just before she dies she lays an egg. Within 3-5 days this egg will hatch and Ryo-Ohki will be reborn. Sometimes the new generation Ryo-Ohki will evolve new abilities. Ryo-Ohki dies twice in the OAV and once in the TV series. Ryo-Ohki died after being shot down by Funaho, Yosho's ship and when Ryoko crashed her into the earth to destroy Ayeka's ship. In the TV series she died in the first scene.
Ryo-Ohki was created by Washu using a simple life form called Mass and an unknown mineral element. Later in the OAV some Mass escape from Washu's lab and gets loose near Tenchi's house. In order to stop the Mass Ryo-Ohki absorbed the Mass themselves. After that she could take on the form that the mass were in, that of a teenage girl that looks a lot like Ryoko. After learning that she didn't know how to walk as a human, she decides to learn the way humans do. She becomes a toddler and grows up.
She draws her power from Ryoko's gems. That explains the gem on Ryo-Ohki's forehead. The gem is what keeps Ryo-Ohki alive. It allows her to communicate with Ryoko when she has at least one gem. The gem can also emit a powerful laser which is her primary weapon in spaceship form and can be fired in cabbit form too. She can use telekinesis to make herself fly as well as other objects.