Is there such a thing as a Seijin in the future

Dec 10, 2017
U.K scotland
there is a program that iv been watching called skyland its an animation about the 23trd centenary which they have no water and they live in houses on floating blocks in the air and there a thing called a Seijin which is in the title and i want to know if that is a prediction or a real thing i no its just a cartoon that i have seen too many lol
thanks cupcake