The Choushin or Chousin (Super God) are a trio of hyper-dimensional deities responsible for the creation of the multiverse and all of the higher dimensions of existence.
(There are 22 known Dimensional Supervisors, with each reigning over ascending dimensional space. For comparison, our universe has only 4 commonly observable dimensions, with the existence of higher numbers of dimensions being a subject of scientific inquiry.)
They are essentially Omnipotent, Omniscient, and Omnipresent, only surpassed by Kami Tenchi. The Choushin consist of Washu, Tsunami, and Tokimi.
At some point, the sisters became aware of the possiblity of a higher power or Kami (God) greater than themselves. Just as Dr. Clay's robot Zero couldn't prove the existance of Tokimi when she saw her, the Choushin couldn't prove the existence of a being higher than they, nor could they create such a person. The sum total of creation was started by them after an unknown length of time spent trying to theorize the existence of such a being. They came to the conclusion that a more practical approach was needed. Each sister took a different route in reaching this goal.
Washu, chose to seal her godly powers and consciousness into three gemstones. She had no memories of anything prior to showing up at a monastery on the planet Kanemitsu in the third dimension and then set out to learn everything that could be learned from scratch. The purpose of Washu forgetting everything was so that she could relearn and thus try to prove the existence of a higher-level being, something impossible when she knew everything, thus this allowed her to think outside of the box. With this approach, she hoped to find the kami, becoming the universe's greatest scientific genius in the process. With her brilliance, Washu created powerful beings Ryoko and Ryo-Ohki as entities capable of harnessing the great power of her mysterious gems.
Tsunami chose to conduct her experiments in the 3rd dimension as well. Using her own existence, she literally planted the seeds to create a new type of life - the Royal Trees of the Imperial Family of the planet Jurai. Possibly knowing that he would find her, the man who would become the first Emperor of Jurai stumbled upon a sleeping Tsunami who had been asleep so long on the planet that parts of her began to trun into a tree. Tsunami saw potential in him, and theorized that a superior life form would be born from him or his descendants. Thus, she gave him the seeds of the Royal Trees which became the greatest force in the galaxy, being the only entities that could generate the Light Hawk Wings, the manifestation of godly power in this dimension. Tsunami swore to protect him and his descendants as the patron goddess of Jurai while she waited for the birth of princess Sasami whom she was destined to merge with, as well as the kami/God that the Choushin sought out...Tenchi.
Tokimi followed the original plan and distorted the harmony they had created in the multiverse (the multiple dimensions of the universe). She did this to cause anomalies and abnormalities from which she hoped the kami would emerge. Z was the result of her actions and Tokimi took him as he was the greatest "potential" she'd found. (A potential, being the only beings that can generate the Light Hawk Wings other than the Royal Treeships).
Though each sister is successful in finding and/or creating beings that are capable of wielding their power, they had yet to truly discover the one who is even more powerful than they. Tenchi is this aforementioned being. His power barely tapped into, Tenchi might just be the very most powerful being ever.
The Choushin considered (past tense) Tenchi to be another potential (albeit the best one due to his matter conversion ability), but Tsunami and Washu decided that they cared more about Tenchi as a person than whether or not he was the superior hyper-dimensional being they've been searching for for millenia. After Tenchi killed Z, it became apparent that Tenchi was indeed the being that the Choushin were looking for. However, as Tsunami and Washu stated, really finding out his origins and purpose should be fun and not rushed, and therefore will continue to live their lives on Earth with Tenchi.
Though the " Counter-Actor" is also a factor. The counter-actor is the sentient counter-force to the Choushin. It is revealed that the counter-actor is actually Juraian Empress Misaki Jurai, the mother of Ayeka and Sasami, who somehow becomes this formidable being filled with rage who is a major threat to all of existence. Misaki becomes the Counter-Actor in the distant future after her husband Azusa and sister/co-wife Funaho have died, and she grows unstable due to the loss of them. However, Kami Tenchi is able to effortlessly stop her.
The Counter-Actor is the sentient sum total counterforce to all of the Choushin's actions. There has to be a counterbalance - for every action, there must be an equal and opposite reaction.
The Choushin are stated to be true hyperdimensional deities, shown as enormously larger than all of existence combined, beyond physics, beyond scientific definition and dimensional scale, the creators of an infinite number of higher-dimensional experiments and completely beyond all of existence.
If you want the more indepth explanation for how this works, infinity in projective geometry states that each higher-dimensional space is infinitely greater/more powerful than the preceding number. For example, as Brane Cosmology and M-Theory state that multiverses contain 10-11 dimensions in sum total, the 22-dimensional space ruled over by the Ds is at least infinity raised to the power of 11 times greater than multiversal scale.