From a dream of mine, the main story is that the world is divided into 17 layers, one world per layer, and the worlds are connected to each other without interfering. When qualified people appear in the world on each layer, then these qualified people can go to the higher-level world. At this time the gatekeeper will appear and lead them to the entrance.
But once you enter the new world, all memories of the previous world will be forgotten. In order to help the qualified person better integrate into the new world, he will retain his original knowledge and have his own circle, as if he has always lived in this world.
This story is about the gatekeepers.