Tenchi Muyo! Ryo-Ohki
The first mention of Lady Tokimi is during the OVA 1 special where Sasami has a nightmare in which Tokimi is trying to kidnap Tenchi. Lady Tokimi then appeared in the OVA 2 as a mysterious divine being ordering Dr. Clay to abduct Washu Hakubi, the universe's greatest scientist, for mysterious reasons.
It is revealed that Washu and Tsunami are her sisters and together, the trio created the universe and its many dimensions. Over countless millennia, Tokimi generated abnormalities in the universal fabric, working with and apart from her sisters in order to find a theoretical being more powerful than they.
Although Tokimi was shown to coldly play with the structure of the universe, including moving galaxies and creating great anomalies/space distortions, Tokimi is not shown as an antagonist to the main cast in the 3rd OVA, since she sees Tenchi Masaki as the result of her and her sisters' search to find the aforementioned higher power.
While Washu and Tsunami eventually went their separate ways to bring about the higher being, Tokimi remained to carry out their original plan: creating chaos in the universal fabric to create this super being or cause it to reveal itself. It was through her manipulations that the man Z gained the power to generate the Light Hawk Wings, manifestations of godly power in this dimension. However, she also saw that Z was unstable and wondered if her sisters had better success. That was the reason why she wanted Clay to bring Washu to her. However, Clay's ulterior motives left her no option, but to have our dimension's supervisor D3 seal away Clay's memories of their interaction.
Later, when Z rebelled against Tokimi and tried to kill Tenchi, she sought to contain her errant servant. But because of this, when Tenchi's godly self emerged from his mortal shell and his powers threatened to destroy everything, Tokimi and her reunited sisters tried to contain it. However, Tokimi was attacked by a being called the "counter-actor," the sentient counter-force to the Choushin, who cared nothing for the universe and only wanted to cause destruction and death.
The "counter-actor" was revealed to be the Empress Misaki Masaki Jurai gone mad. Kami Tenchi later saved Tokimi by calming the rage of the counter-actor. In the conclusion of the situation, Washu and Tsunami expressed their delight in interacting with the characters, especially Tenchi. Tokimi felt regret not having the same interaction with Z during her own experiments, and upon releasing Z back to his happiest place and time, expressed a bit of hope that the two of them might one day meet again.
Tokimi transforms herself into a "chibi" form while at the Masaki residence. She shows great interest in the antics of the household, and in this form she shows a more friendly and carefree nature, despite being very ironic. Tokimi, in her normal form, was a guest at the wedding of Nobuyuki Masaki and Rea Masaki, occupying the "resident kami" portion of the Masaki shrine. When asked as to why she was there, she simply replied that 'where else would a goddess be?'. She then added that there was a reason for her action, but when asked what it is, she replies that it's a secret. Tokimi stays in the shrine whenever she is not in the higher dimension.
After the revelation of Rea Masaki's background, Tokimi was asked to keep an eye on things in her native universe. Eventually she was tasked with sending Tenchi's younger half brother, Kenshi Masaki, to Geminar, starting the event of War on Geminar. She also promised that, should Kenshi ever be at a point where he 'would' be killed, she would save his life and take him home, on the condition that after doing so, he would never be allowed to return to Geminar.
Some fans have theorized that Kenshi could possibly be the reincarnation of Z. The reason for Tokimi being present in the resident kami section of the shrine during Nobuyuki and Rea's wedding could be that she was blessing them with a child; Kenshi. It could be possible that she remained at the Masaki home in order to watch over Kenshi, and eventually sent him to Geminar, a world where one of his parents (thought to be Rea) originally came from. And because she intended for Z to go "home," Geminar could also possibly be Z's homeworld. Though this is all theory, as mentioned before.
Tokimi is currently the most powerful of the Choushin sisters, evident because she has the ability to cut both Washu and Tsunami off from their power. In OVA 3, it is revealed that Tokimi was in charge of limiting the Choushin's power since her sisters were operating in a lower dimension. This limiter could be removed in an emergency and since the limiter was removed at the end of OVA 3, it is unknown as to who is the most powerful or if three are simply equal in power. However, Tokimi is the Battlemaster of the Chousin, so she is presumably the most capable in combat.
At some point in the future, Washu and Tsunami will convince her to fully descend to their dimension in the same way they have. Her personality becomes one of an obstinate "little sister" for a while, until calming down amd enjoying her new existence.