Here is the base plot of a story.

At some random point in time, "something" happened, and the world was broken. It's unknown what happened, and hypothesis were created that it could have been something from the future, like the destruction of the world or the universe leading to side-effects in the present or something unexplainable like that, but everyone understands that their guesses are more based on fiction than in science, that's how abnormal is the situation.

When it first happened, many people were separated from each other, and confused about what was happened, they could be with their families in their house, and suddenly, they would be alone in the same place, with everyone else gone, and no explanation at all. But maybe as fortune had it, there were points of contact in these fragments of the world, and one of them were things outside the atmosphere, like satellites, so information propagated through them could be received, and thus information could be shared among everyone.

And that's when the 2nd surprise, and to many, horror, of the discovery of what happened.

The world had, for a lack of a better analogy, been divided into multiple parallel worlds, and people were separated semi-randomly, so even if there was a family living in the same house, each member could have been transported to a different parallel world, while they remained in the same house. And then they found that traveling among these parallel worlds was not impossible, rather, it could be quite easy, but that's where the unbelievable happened: The parallel worlds and those living in them looked the same from their own point of view, but had completely different scales compared to other worlds. This meant that a person could move to a different parallel world, and either be an unbelievable giant, or smaller than a small animal.

Thus a term was created to define them: Class.

Those of a higher class could more easily move between the worlds, and were extremely large. meanwhile the lower class were more numerous and had more difficulties moving between worlds, however, they were so small that moving to a higher class world caused them to be almost insignificant.

When a girl from the Highest Class world got to open a rip in space that allowed her to visit the lowest class world (that she didn't knew what it was), her face appeared at the height of the clouds, and her height was measured to be around 10Km tall, meaning that if she decided to go in completely, her steps would shake everything in the surroundings, and inexplicable destruction would have happened. Fortunately, the finding was reported on the media, which the person was listening, and she stopped. By now, everyone is already aware of the dangers of crossing to a different world.

Besides this spatial related effects, there are also strange time related ones in difference, for example, things take much longer to go bad in higher class worlds, it's suggested that bacteria and viruses all ended up in the lowest class, thus the air of the higher classes is much cleaner, and food hardly ever goes bad. This is important as the higher class people are very few individuals, and they would be unable to sustain themselves in the lower class worlds.

Once a rip in space is created, it's almost impossible to close them again, however, they can be moved to more convenient places, so those of higher classes have created entries for lower class people, so for example, a small metropolis could then be connected to the table of a higher class person.

Despite the dangers of moving across worlds, there were necessities and convenience in doing so, but this can be better understood by seeing how people had been divided.

The number of specific worlds is unknown, as there could be empty ones, however, there are a number of them that are either more populated or more influential.
From lower to higher class, and how large in average they are in comparison to a normal person:

- 30cm tall: Lowest class is said to have everyone with mental deficiencies and irritating personalities. It's a world that, when was found out, people decided to just leave them by themselves and stay away. They only complained while destroying everything unimpeded. It was decided to leave them alone as they would be a detriment to any society.
- Normal size: All human males along with all complex living beings like animals, bugs, fishes and birds. They are the most populated world.
- 5m tall: Older women and those of lower beauty standards.
- 20m tall: General women that don't fit the higher levels, most Beautiful and good nature people from China and Africa
- 50m tall: The most beautiful and good nature people from China and Africa, and most Beautiful and good nature people from the other countries other than China, Africa and Japan.
- 100m tall: The most beautiful and good nature people from other countries other than China and Africa, and most Beautiful and good nature people from Japan.
- 200m tall: The most beautiful and good nature people from Japan.
- 500m tall: Selective female personalities of influence in the world. There are however a few that suffered side-effects, losing control of their limbs, requiring help to even move.
- 1Km tall: Selective women and girls of good nature and beauty.
- 2Km tall: Even more selective cases of women and girls
- 5Km tall: Even more selective cases of women and girls (no more than 50 exist around the world)
- 10Km tall: Even more selective cases of women and girls (no more than 10 exist around the world)

Among the necessities for having to cross worlds is the obvious situation of having to contact others from lower class worlds. It's not uncommon for there to be women the size of buildings navigating on the world where males are, these males could be the woman's parents, brother, sons, or even just friends from before the event that separated the world. Those of lower class worlds can also go to higher class worlds, although everything would look proportionally much bigger to the point that they would require assistance of the locals (giantesses).

Among the conveniences of crossing worlds, one of them is that those of lower class could essentially have infinite resources on the higher class world, so if they need any sort o resource like metal, a small stone in the highest class world would be akin to a small mountain for the smaller one. And there is also the convenience of traveling. Someone from a higher class world could certainly cause some incalculable damage just by being, however, the portals to cross worlds happen in the same relative position on both worlds, so if you open a portal inside a house in the higher class world, another portal will appear at a certain height above the same position of that house.

So if someone of higher class wants to cross a continent, it would be easier for them to cross worlds on their current position for a lower class world where everything is super small, walk to where she wants to go (someone 10Km tall for example could cross the ocean by walking), and when she reaches her destination, she cross back into a higher class world, slowly fixing her destination as she moves across higher class worlds. This is the only way for many of the women of the higher classes to meet each other, as they were left in fewer numbers in their class of the world, meaning the world is pretty much empty.