Tenchi Muyo!

[Archangel]

Tenchi Muyo! (天地無用! Tenchi Muyō!?), is a Japanese anime, light novel, and manga series created by Masaki Kajishima and Hiroki Hayashi.

The generally accepted translation of the title is No Need For Tenchi or Useless Tenchi, though at the time of its appearance it was also translated variably as No Heaven and Earth and This Way Up due to the original title's pun nature and multiple meanings.

The original series began with a six episode OVA called Tenchi Muyo! Ryo-Ohki (天地無用! 魎皇鬼 Tenchi Muyō! Ryōōki?) released in Japan on September 25, 1992. As its popularity grew, it spurred a seventh episode titled Tenchi Muyo! Special: The Night Before The Carnival (also known as the Tenchi Special) and a stand-alone Mihoshi Special. The second OVA series was directed by Kenichi Yatani and released on 1994, featuring episodes 8–13. The third OVA series was also directed by Kenichi Yatani was released on 2003, featuring episodes 14-19 followed by a special twentieth episode.

A twenty-six episode TV anime series called Tenchi Universe (天地無用!宇宙篇 Tenchi Muyō! Uchū Hen?) was released on 1995 retelling the original story, documenting how everyone met and changing the back story of some characters.

Tenchi in Tokyo (新・天地無用! Shin Tenchi Muyō!?) is another alternate version, chronicling Tenchi Masaki's move to Tokyo.

Additionally, there are spin-off series (such as Magical Girl Pretty Sammy), as well as spinoff manga (as the anime preceded the manga). The franchise has also spawned soundtrack CDs and other merchandise released both in Japan and in the United States.

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Incest the animu, who's watched it?

[Kraco]

Come on, who hasn't watched Tenchi Muyo? It's a basic classic.

Although I'd most poignantly advice against Magical Girl Pretty Sammy. It's an old story, but it killed the whole magical girl genre for me for a while.

[Archangel]

As always, you assume everyone to be as ancient as yourself Kraco

I'm currently trying to acquire Tenchi Universe and hoping it will shed some light into the overall plot which was pretty god damn confusing in the 3 OVA series

[Dark Dragon]

Tenchi OVA 1-3, GXP and Saint Knight's tale all follow the same continuity.

Universe follows another and synch up with daughter of darkness and Tenchi in love.
Tenchi in Tokyo is a spinoff with a completely different story.
Tenchi Forever is a standalone movie that is base on the series but isn't really related.
Pretty Sammy and every other mahou shoujo related show is yet another spinoff that you should just really avoid.

Watching Tenchi Universe won't makes the OVA story less confusing. What you're looking for are the databooks that Kajishima release periodically that give background informations, but good luck finding the translated version to them all.

Tenchi Universe is directed by Hiroshi Negishi and he pretty much just took Kajishima character and created a show around it. It's generally accepted among the fandom that Universe sucks and Kajishima hated Universe so all of his later works are based on the OVA storyline.

You can pretty watch the OVA > GXP and Saint Knight's Tale and not missed out on anything. I personally hated Tenchi in Tokyo and didn't care for Universe.