There are two types of worlds. One is the world we see, where humans, ghosts, gods, and various animals live together. The other is the world where humans are not humans, ghosts are not ghosts, gods are not gods, and things are not things. People call this the "anti-world."
If you try to come to another world, you will see another self, but it is not exactly the same. He may be powerful or extremely weak.
In short, he has everything you don't have, he hates everything you hate, and he loves everything you love. He seems to be the same body as you but not the same body, and he lives and dies with you.
Of course, there is a clear law that no one is allowed to try to enter another world, because once the door to another world is opened, it cannot be closed for three months. During these three months, things inside can come out and things outside can go in.
However, as time went by, the existence of the two worlds was gradually forgotten and became an unverifiable legend.
That year, I was ten years old. We lived in a small village in the mountains. I had two friends, Amin and Mikasa. There was a big forest behind the village. I still remember that we played hide and seek there that day...