How it would be introduced:
The train network would be first introduced at the beginning of the Mugen Train arc (If there is a story mode) with you and your friends (If you have any) buying their tickets and boarding the train
How it would work:
The train network would consist of several main train stations spread across large cities/towns, when first stepping onto the train station there will be a man in the booth selling tickets, and of course these tickets would cost money, once you buy your tickets, there will be a cutscene of you boarding the train and walking into the desired cart of your choice, this is when you would once again be able to control your character and you could walk around in the cart will several booths for you too choose from to sit in, once you have chosen your desired booth to sit in you could play mini games that give tiny amounts of exp while you wait. There could also be a small chance of demons attacking the train and crashing it, if you defeat the demons attacking the train you get a large sum of money and exp, once you choose to exit the crashed train another cutscene would play of you exiting out of the crashed train as it then spawns you in by the crashed train to where you would once again take control of your character, if your train ride is successful you exit off at the train station of your choice and carry on with your journey.
How you could gain access to the Train Network:
After completing the Mugen Train arc you would then have access to use the Train Network to travel where ever you want on the map in a timely fashion.