He - traveled through time...
A month ago, he inexplicably came to this backward era that has not yet entered the Internet, and turned into a little boy of only seven or eight years old. What he saw flying in the sky may not be birds, but people flying around on swords. What swims in the water may not be fish, but may also be Dai Nasou (monsters). If he is not crazy, then the world is crazy!
Concept: Everyone is their own protagonist.