A portal to another dimension is suddenly discovered. What spread out beyond the nondescript door was a parallel world with a history different from this one. This year marks 50 years since the world behind the door was named "PORTAL" and observations of its interior began. "PORTAL-X" is a program that has been broadcast for many years with the aim of utilizing the failure cases of various portals in our society.

Kaif is a new program director who reports on all sorts of parallel worlds, and Luna is a program cameraman. The various parallel worlds and portals that the two of them cover are all worlds where people have made wrong choices at turning points in history and have fallen into irreversible situations. What is shown on camera are food shortages, a world where immortality has been achieved, a society that has not achieved true diversity, an extremely low birthrate, and a world that relies entirely on luck.