So I hear there has been some confusion about the correct order of the several Tenchi series. So allow me to explain.

The first series created was the original 3 Tenchi Muyo! OVAs. It is also known as Tenchi Muyo! Ryo-Ohki. It has 20 episodes and has been aired on Toonami several times. In this OVA, Tenchi has special powers, unlike the second series.

-The first OVA is episodes 1-6.
-Tenchi Muyo! Daughter of Darkness*
-Episode 7 is a special.
-Episodes 8-13 are OVA 2. (Including the bonus episode 13.5)
-Episodes 14-19 are OVA 3.
-Episode 20 is a special.

*The movie Tenchi Muyo! Daughter of Darkness takes place after the first OVA and ignores the second and third OVAs.

The second series is called Tenchi Universe. This series is similar to the first, except that other than the Jurai power Tenchi wields through Sword Tenchi, he doesn't show any special Jurai powers throughout the series. Tenchi Universe has 26 episodes and has also been aired on Toonami more than once.

The movie Tenchi Muyo! in Love takes place after the conclusion of Tenchi Universe.

The movie Tenchi Forever! takes place after the conclusion to Tenchi Muyo! in Love. This movie is also known as Tenchi Muyo! in Love 2.

The third series is Tenchi in Tokyo. This series is completely different than the previous two series. Tenchi moves to Tokyo, and falls in love. However, a powerful imprisoned demon is intent on destroying Tenchi and all of his ancestors. Tenchi in Tokyo also has 26 episodes.

The fourth, and currently final Tenchi series is called Tenchi Muyo! GXP. This spin off is set in the Tenchi universe, but has a completely separate storyline focusing on completely different characters, loosely based on the original characters. This series is about the Galaxy Police, and has 26 episodes.

I hope this helps. :D If you have any questions, feel free to email me at