Jurai is a planet located in the Milky Way, and also the name of its royal family.
The Juraian empire came into existence when the man who would become the first emperor of Jurai stumbled upon a sleeping Tsunami-kami-sama. She then promised to protect the Masaki line for generations to come. It should be noted that Tsunami seemed to have been at that spot a long time, no doubt due the Chousin's ability to see ahead into the future.
The planet Jurai is ruled by a royal family, the Imperial House of Jurai (樹雷皇家) all of whom take "Jurai" as part of their names after bonding with one of the royal trees. The most notable of them is First Princess Ayeka Masaki Jurai, the current crown princess of Jurai. She is the daughter of the Emperor of Jurai, Azusa Jurai. Azusa Jurai's two wives are Funaho Masaki Jurai, First Queen, and Misaki Kamiki Jurai, Second Queen.
The child of Azusa Jurai and Funaho is Yosho, a.k.a. Katsuhito Masaki, who is Tenchi Masaki's grandfather; the children of Azusa Jurai and Misaki are Ayeka and Sasami Masaki Jurai, who came to Earth to look for Yosho when he disappeared.
Other members of the Jurai family are Seto Kamiki Jurai, Misaki's mother, and Noike Jurai, Seto's adopted daughter.
There are four royal houses on Jurai, these being House Masaki, House Kamiki, House Tatsuki and House Amaki. Probably the most famous house is Kamiki, this being that it has the famed 'devil princess of Jurai', Seto Kamiki Jurai. Seto is also the reason House Masaki are current rulers as she stopped the house from becoming extinct when numerous members kept running away or left Jurai. House Amaki is currently a bitter rival of House Masaki. The intentions of House Tatsuki are still unknown.
The planet Jurai is home to a species of intelligent trees, the Trees of the Imperial House (皇家の樹), descended from the goddess Tsunami-kami-sama. In fact, the name "Jurai" is a combination of the kanji 樹 tree and 雷 thunder. These trees are capable of bestowing great powers and long life to those Juraian royals who are partnered with them, and are activated by special devices known as keys. These trees are also used to provide power to Juraian spaceships. All power supplied to the tree ships comes from Tsunami-no-ki from a subspace network.
Juraians are also feared throughout the Galaxy for their superhuman strength, plus the ability of Juraians of noble heritage to summon force fields and discharge energy blasts. Royal Juraians are also known for their extremely long life spans, as Ayeka looks about the same age as Tenchi, but she is much, much older than he is.