D is a bioroid, an artificially constructed biological/mechanical being first introduced in the Tenchi Muyo! universe. The war between the Earth Defense Force and the Rara Army began when D and at least two mechas were discovered in an artifact of unknown origin. Her original body was damaged, so a bioroid was built to contain her essence (represented by a glowing orb in place of an eye) while her body healed.        D appears to be as inhuman as the robot she pilots, speaking mechanically and asking many questions about human emotions and behavior. The only one to break through her stony exterior is Kazuki, to the shock of Commander Sanada. D frequently has visions of a horrible creature attacking, and is deathly afraid of Himiko.        She develops a strong attachment to Kazuki, culminating in her decision to return to her real body at the climax of the series in order to save him. It's revealed that D stole Zinv and fled her world to escape Himiko and Kumu, who claimed the lives of her friends.        As a robot pilot, D is subpar, often requiring rescue by Kazuki and Mitsuki. However, she redeems herself by removing the limiter placed upon Zinv, allowing its true power to manifest itself.        When Zinv is destroyed and the worlds merge, D becomes Dee Sanada, taking on the animated personality of a young girl.        There is also an apparent resemblance between D and Tenchi Muyo! GXP character Neju na Melmas, leading some to believe that she and D may belong to the same race.  ~taken form wikipedia

Kazuki Yotsuga is your regular average nerd in high-school, except he isn't smart. He has this website which relates to his visions that only he can see. His vision's are about robots who keep fighting each other battle after battle. One day he is sent to a, "parallel world" where these visions exist and he joins a company to fight back against the devious RaRa, who want to take over the world. 
(Source: Anime News Network)

Peace has been brought to both earths, and everyone is living out their lives as normal citizens. But how normal could life be for war hero Kazuki living with five beautiful women under the same roof... Apparently, he doesn't need to wait long to find out. An ancient artifact that is the key to their adventures in the parallel universes forces Kazuki to hop in the saddle yet again, but this time it's outer space or bust. 
(Source: Anime News Network)

2022 marks the 30th anniversary of the original Tenchi Muyo! Ryo-Ohki OVA series and to celebrate, a brand new Tenchi Muyo! GXP anime series was announced. 
The new series, titled Tenchi Muyo! GXP Paradise Beginnings Arc, connects the 4th and 5th seasons of the series and will serve as an introduction to the Paradise War through the eyes of Seina Yamada. 
 
(Source: Crunchyroll)