The demonic space criminal Kain has escaped from prison and destroyed the Galaxy Police headquarters. To ensure that the Jurai will not stop him, Kain travels back to 1970 to eliminate Tenchi's mother before he is even born. Now, Tenchi and the gang must travel to the past to stop him before he ceases to exist.
One day, Tenchi disappears in the forest near his house. Six months later, Ayeka and Ryoko locate Tenchi living in a city, but with a mysterious woman. What's more, Tenchi appears to have aged several years. Whenever Ayeka and Ryoko catch up to him, he disappears into thin air, apparently existing in a fabricated alternate dimension where he has no knowledge of his past.
Mayuka is a girl who appears one day and claims to be Tenchi's daughter. As the initial shock wears off, everyone in the Masaki household gets used to Mayuka's presence. However, things only become more interesting as Washu tries to discover Mayuka's background. What Washu found involves demon, the Prince of Jurai, and unrequited emotions.
The story is set in an alternate world called Geminar, where countries have fought endless wars with replicas of humanoid Seikishi weapons that they found in ancient ruins. 15-year-old Kenshi Masaki, the half-brother of Tenchi Muyo! protagonist Tenchi Masaki, is summoned from another world to Geminar.
Tenchi is an average guy who just accidentally freed the space pirate Ryoko after 700 years of captivity! Attractive alien girls from all across the galaxy are about to descend on Tenchi and make his life more outrageous than ever imaginable!
Seina is unlucky, so unlucky that when he stumbles upon a recruiter looking for his senpai Tenchi he gets taken instead. Forced into the Galaxy police, his luck begins to change. A natural to randomly jumping near pirates, he is assigned his own decoy to draw out pirates. His luck brings him into the lives of four women who have a habit of cancelling out his bad luck, turning it into good. Armed with this luck, they pilot the most powerful ships in the Tenchi Universe to defeat the Barta pirates. Now the only uncertainty is whether the sexy Kaunaq, a former model turned GXP officer, sturdy Kiriko, who has known Seina for years, the mysterious Ryoko, a former pirate named after the legendary one, or the childish Neiju, a powerful witch, will win Seina.
Tenchi Masaki may be a 17-year-old young man in rural Japan, but little does he know how bad his day will be getting. When a space pirate chased by a pair of Galaxy Police officers crash-lands at his grandfather's temple, Tenchi is sucked into a new adventure that will literally blast him off into outer space and beyond.
Shin Tenchi Muyo! is a Japanese anime produced by AIC, aired on TV Tokyo from April 1 to December 23, 1997. It is the third installation of the Tenchi Muyo! line of series, preceding Tenchi Muyo! GXP and succeeding Tenchi Universe. The show was localized in North America by Geneon Entertainment as Tenchi in Tokyo and aired on Cartoon Network from August 25 to September 29, 2000.