1. World Construction
Ever since the City World came to be, many different worlds have existed and been destroyed. However, it has been mostly proven what kind of world it was based on.
That world is tentatively known as the Foundation World.
As the name suggests, the Foundation World acted as the foundation of the current world and it is thought to have had a similar flow of history. The Foundation World is broadly divided into four eras:
-Forth
-Ahead
-Edge
-Genesis
These four eras are connected, but the Foundation World was destroyed at the end of the Genesis World.
After the Foundation World’s destruction, the world was experimentally recreated and destroyed again and again in search of a world that would not be destroyed.
This significant wandering era was a great obstacle to the world, so it is known as:
-Obstacle
During this great obstacle era, either the world got tired of being destroyed or there was some other reason because a world made not to be destroyed was finally created.
And that is the City World that we live in.
It is known as:
-City
Now, let us look briefly over those six worlds.

2. Forth
The pre-hope era.
This was the calmest era of the Foundation World. There were plenty of wars, but it was peaceful on the macro level and the only crises were on a regional scale.
It had little individuality, but it was likely an era focused on personal points of view.

3. Ahead
The progress era.
The Foundation World began to change during this era, but the reason is not well known.
All we know is that various things and technologies began to exist at around this point.
Bipedal humanoid machines.
Large aircraft.
A world of electrical signals and the technology to reach other planets.
The existence of other races, bodily modifications, etc.
It does not seem these things initially existed in this world, but it is not known where they came from. For this reason, people were not able to make these technologies entirely their own during this era. They used them as if borrowing them, they imitated them, and they researched their foundations.

4. Edge
The cutting-edge era.
As people grew more and more used to the technologies gained during the Ahead era, they abandoned the earth for some reason and went into outer space.
The details are unknown, but a single star system caused a rebellion for some reason. In this era, the ether-like fuel source that was discovered during the latter part of Ahead became widely used and the technologies researched during the Ahead era were created to suit this world.

5. Genesis
The great foundation era.
In this era, people returned to Earth.
For some reason, people became unable to use most of the old technology and primarily used the technology gained during Ahead and Edge. This resulted in that super technology fully belonging to the Foundation World. They began to produce for themselves what can be seen as the foundations of what exists in this City World.
The earth was forced to revert back to the dark ages, but it recovered afterwards. However, the war that caused the end of the Edge era restarted and the world was destroyed.

6. Obstacle
The great obstacle era.
Some unknown means were used to create several worlds based on the destroyed Foundation World and they were repeatedly destroyed.
The aim was to create a world that would not be destroyed, but these strange worlds in which a few materials were removed or added to the Foundation World all ended up being destroyed.
Originally, this was thought to have been a single world, but investigations show an uncountable number of worlds were created one after another and each one had its history proceed to the level of the foundation era.
More about each of those will likely become known in the future.

7. City
The city era.
Or perhaps it should be called the City World. This world was created during Obstacle as a world which could defeat the power that leads to destruction.
In the name of progress, the City World gathered the technologies from the Foundation World and all of Obstacle. Currently, City original technologies are being produced as well.
The protection put in place when this world was constructed seems perfect so far, but this has become a world of self-responsibility where the residents try to do something about it for themselves.
Well, even now there have been times when the destruction of the world seemed only a step – or maybe even less than that – away from destruction, but it seems someone has always thrown a punch to correct things.
Perhaps that is because the destruction of this world would mean your very existence has lost. That is a good reason to put some effort into it. I wonder if there is anything good about doing that. Yes, I’m sure there is!
Okay, everyone. Do your best with whatever until we meet again.