The religion, "Airai".
This religion was spread all over the galaxy and the number of it's members surpassed the population of the largest country. It was the largest religion in the galaxy. But one million years ago, it was one of many religions in a single country. Until, a discovery of a fact had changed the situation, and the number of it's members drastically increased in no time.
The fact was related to relics, which existed on the planets all over the galaxy. Each relic was related to other religions and was made by outsiders. From these relics, the natives made up new religion of their own.
After the galaxy academy was founded, many countries started to communicate with each other, and resulting from this, the researchers of the academy discovered that all of the relics, existing on each planets, were common. Though there was one question left, 'Who built these relics?' Of course this question was not only for the researchers but also for the natives of each planets. They started to announce that they were the origin of this original religion. As the time passed, this debate was amplified and sometimes even war broke out between them. 1000 years later, a research team lead by Washu found the roots of the relics. That planet was Airai. All the religion derived from the relics, and were all related to the religion of "Airai". For this reason, this religion spread through out the galaxy in no time.
Another important fact, the relationship between Airai and Jurai. In most of the great power countries, had an outpost for Airai existed. Of course Jurai also they had the freedom to choose which religion they believed in, and as a collective of dozens of nations, there were many religions in Jurai when it was first started. However, in the present, all of the religions have disappeared and only few were left as a part of customs. This included the largest religion "Airai", too. There was almost none that believed in "Airai" in Jurai.
There were several reasons for this. One was that, as Jurai was formed by colonists, it was rare for them to find a new relic and make it in to new religion. Another is that Jurai was located far from Airai, scarcely any relics existed.
However, the largest reason was that they had their own distinct object to worship.
It was the Royal trees all born from primogenitor "Tsunami".
The formless God of Airai and an existing God of Jurai. It was natural that Jurai would not accept the religion of Airai.
However, the definitions of God here were different from what Earthlings like Tenchi believe in. The God they said was awe the supernatural like, aliens who had the technique of flying between stars, a different dimensional life form and a high dimensional intelligent life form. At this point, what they call God is not the same as what a prime-intelligent life form believe in. Among these, the high dimensional intelligent life forms have an overpowering force, so even now where advanced science is developed, they still are called Gods.
Due to the existence of the Royal trees, the manifold religion, which existed in the prime age of Jurai, converted to Royal tree worshiping for several hundred thousand years.
It was natural for the people of Airai to take an adverse position to Jurai and called them heretic. Recently some of the hard cores started to prohibit Jurai's Imperial ships from entering their territory. On the other hand, in Jurai, some people also started to insist that they must revolt to these actions.
The relationship between Airai and Jurai was very complicated. Airi and Yosho met each other during these tough times.