The story takes place hundreds of years later, with a group of people returning to the home planet of mankind, the Earth, and the secrets of the Earth and the rise and fall of civilization.
————————————
The ancient prehistoric civilization survives under the protection of the earth's core.
The persistent and mysterious girl has been searching for her sister's soul for tens of thousands of years.
The four-dimensional civilization brings not only endless time, but also endless pain.
This is an exchange of civilizations from aliens settling on the earth and aliens from the earth settling in the stars.
————————————
The main line of this article is BG, but there are still BL and [hidden] GL, so I don't like to stray into them.