Z (ゼット Zetto?) (real name Z-0001332536893) is the principal antagonist of the third OVA series of Tenchi Muyo! Ryo-Ohki, though his first on-screen appearance (albeit in silhouette only) was in the final minutes of the second OVA's "Zero Ryoko" and the short clip "Here Comes Jurai, Part 2".
Z is a being of great power, even capable of punching holes through planets seemingly without effort and can destroy large, powerful star fleets without much effort. Like Tenchi he can produce kō-ō-yoku ("Light-Hawk-Wings"), five of them to Tenchi's three. However, Z's strength would never have equaled Tenchi's; while he commands two more Light-Hawk-Wings than Tenchi, Z does not possess Tenchi's power of Material Conversion (which allows energy to be converted to matter, and vice versa).
Z was originally an expert space fighter pilot. He, his family, and many other members of his people found and attacked the "temple" (for lack of a better term) where the Choushin are. This attack was most likely set up by Tokimi's experiments to look for potential of a greater power being (kami) in the universe. During the battle, the cruiser containing his family was destroyed and he was injured severely. Watching his family die caused him to unleash his untapped Light-Hawk-Wings for the first time, which he used to heal himself and destroy the enemy fleet. It was at this time that Tokimi noticed him and he came into her service.
Serving Tokimi, he then takes on the role of the battle machines that he and his people had fought and lost too. With his five Light-Hawk-Wings, he is easily able to overcome other races who send war fleets to attack the "temple." Again, this is done so that any being with the potential of producing Light-Hawk-Wings on their own will emerge from the battle.
During a meeting with Tokimi and the Dimensional Supervisor D3, he notes that Dr. Clay has discovered the third dimension location of her older sisters Washu and Tsunami. It is here that the events of OAV 2 Ep. 5 (episode 12 overall) where Tenchi Masaki uses his own Light-Hawk-Wings to overcome a dark hole are noticed, as is the uniqueness of Tenchi's power.
Knowing that Z would likely challenge Tenchi, Tokimi orders him to not touch Tenchi. This is re-enforced with a warning from D3. He decides to obey the letter of the order but not the spirit of it and he tampers with a communication from Galaxy Police Officer Mihoshi to her family, he sets in motion a chain of deadly events that make up much of the story of the third OVA series.
When his attempt to manipulate Mihoshi's brother Misao into killing Tenchi fails, Z attacks Tenchi directly in an attempt to eliminate him. In his mind, he's doing Tenchi a service since he knows that Tsunami and Washu will bring him back to life, only he will no longer be a freak of nature with unnatual abilities. In the process, Z destroys much of the Earth and when testing Tenchi's material conversion abilities, destroys a large section of the moon.
Since Tenchi only displayed three Light-Hawk-Wings, Z canceled them with three of his own, leaving him with two and Tenchi with none. He attempts to kill Tenchi, but Tenchi manages to flee to Saturn. To stop Tenchi, Z has pulled from the future the entity known as the Counteractor who also happens to be Misaki. Seeing this, Tokimi finally made a direct attempt to stop Z. However, Z overcame her efforts with the help of the Counteractor at great cost to himself. He attempts to again kill Tenchi which causes Sasami to become Tsunami. Tsunami and Tokimi's strike clash together, causing much of the galaxy to be destroyed. Washu, who had resumed her Chousin form, put an end to it and focused her sisters' attention. Z explains things to Tenchi, including the story of Z's past. Ryo-ohki attacks Z and is destroyed. Ryoko then attacks Z to save Tenchi. To prevent her from being killed, Tenchi overcomes the Counteractor and places himself between Z's Light-Hawk-Wings and Ryoko.
Tenchi is sliced open by Z's Light-Hawk-Wings, however, instead of dying, a huge burst of energy emerged from the wound. Z was easily destroyed by this surge of Tenchi's power. Z had been so blinded by hatred and anger at what Tokimi (and indirectly Tsunami and Washu) had done to him, combined with his jealousy of Tokimi's clear interest in Tenchi that he failed to notice that even after eliminating Tenchi's Light-Hawk-Wings, Tenchi still survived in the cold vacuum of space.
Later, when the Chousin had explained what had happened, Tokimi realized that had she done things differently with Z, she might have had a relationship with him that was similar to the one Tsunami and Washu had with Tenchi. She then recreated Z as an infant and sent him back into the past. Because Choushin cannot re-create the power he once had, Z will now lead a life as a normal member of his race, and hopefully a better one.