It is said that ancient humans first encountered aliens about 15 billion years ago, after leaving the Physical Realm and becoming a Type V Civilization.

Actually, an encounter with an extraterrestrial being isn't an easy feat.

Of course, it was difficult for a civilization to leave the star system where they were born, but the bigger problem was that it was rare for a lifeform to be born on a planet at a galactic level.

If you wanted to meet extraterrestrial beings (in the case where they did not approach you first), your civilization had to at least reach a level where they could leave its current galaxy without much problem. Of course, it would take a considerable amount of time to pile up a civilization from nothing, but the ancient human race cleared that condition and met up with a new lifeform, the extraterrestrial beings.

However, the first aliens humanity met were also humans.

Aliens, the beings they met in the distant universe, were of the same race as them.

Great confusion arose, of course. They did not know if it was coincidence or fate, but there was not much difference in their level of civilizations, and rather...