Imai has a tendency to not feature a same place twice. The course of story to date has been the following:
-Random Sector
-Church
-Iron Mountain
-Simeon (outside)
-Simeon (inside)
-Unknown place
-Underground city (testament graveyeard)
-St. Rose
-Black Market
-Underground city (city)
-The same sector from the beggining of the story 7 years ago
-Lifiaburg
With the characters is pretty much the same, except for the main staff and some exceptions. When the timeskip happens some if not all these places will undergo some changes. Eventually, the main staff will pay these places a second tour.
Explore fully the vast world you've created yourself is one of the things that makes a story good, and the author knows that. He wants to give his readers wide variety of places and characters, because there'a so many things to enjoy
Btw, it's me guys