Aside from the circles, the train is the link between the earths and Ileosa.
It is basically the method of 'isekai' round here. The train feels like an entity of it’s own, hopping dimensions, from Ileosa to earth, seeking out 1 person per earth version and appearing to them in a time of desperation, where they have no other choice but to enter it, even if trains in that world are not invented, the people are still cornered into taking it as an option. Works in mysterious ways.
The inside of the train’s carriages tends to be mono-colored, matching the soul of the person entering it, if the train picked up someone with the same-colored soul, they will be in the same wagon. You receive a temporary ticket from a dispenser that only really shows you a colored ring(one that will correlate with the ones that will appear on your body the moment the train doors close) and the number of your earth.
The train will then head to a random location in Ileosa’s lawless lands and open one of it’s wagons to let one or two people out before disappearing. It doesn’t let everyone out at once. Keep it scattered y’know. The train has no tracks, it’s lower part being obscured by a sort of hot steam, not exactly dust or clouds.