Let's just say that just as there are infinite cars on this train, there are just as
infinite ideas for fanfics of it.
- The train itself. While we know the train's purpose, there's still the big question of who built it, where it came from, and how long it's existed. The series itself has only briefly touched upon that last one, with a few episodes making it clear in the casual dialogue that the train has been around for a few centuries at minimum.
- What type of people are on the train and what problems are they going through? In addition to original character fics, many fans have also made OCs called "Infinitysona"s
along with a denizen to help them on their journey.- We've also only seen passengers from Western countries. What about those from countries like Japan, which is well known for having many a Rail Enthusiast?
- Seeing that the train is infinite and hosts numerous worlds, coming up with different types of cars for OCs and crossover characters to explore is a fun challenge.
- Tulip has no reflection at the end of Book 1. How will this affect her, and what would happen if others notice?
- What type of adventures will Tulip's reflection go through on the train was this until Book 2 answered it?
- In "The Engine", Tulip uses Amelia's tape to momentarily distract her, but it doesn't work thanks to the intervention of the Steward. Really makes one wonder how she experienced her memories.
- Since Year Inside, Hour Outside isn't in effect on the titular train, how do the family and friends of passengers cope with the sudden disappearance of their loved ones? And how do they react when they return months or even years later or not at all given Simon's fate? Or would they even follow the passengers to the Train because they've disappeared?
- One word: Amelia. Her number is so obscenely high, it begs a few questions: what did she do over the past thirty years to get it that high? What will she have to do to get it down to zero and leave the Train? Is that even possible at this point? Book 3 shows she's now working under One-One as an engineer as a form of redemption, but will that be enough to accomplish her goal?
- Come to the end of Book 3, there are the added questions of her relationship with Hazel. How close do the two of them become? If Amelia getting off the train becomes plausible, how will that affect Hazel if she does become attached to the older woman? Would Hazel be able to follow her to Earth-like Lake did with Jesse or be left behind like any other denizen?
- There are two feuding families in "The Family Tree Car" which makes one wonder why those two families in the Infinity Train exactly? Are they related to the train's construction in some way?
- Real-world knowledge of the train. How many people know about the train? Are there people back on Earth actively investigating it? Word of God has confirmed that it has become a seldom discussed internet myth in the present day, with former passengers occasionally being able to find each other, and that world governments are investigating its existence.
- After Book 4 revealed its protagonists to be musicians, fics where their band is used as a way for former passengers to connect with each other became a popular way to tackle this subject.
- Mace and Sieve were once reflections of other people but joined the Mirror Police so they wouldn't lose their memories. What were their "primes" like?
- The Mirror World in general can inspire this. Did Lake's successful escape have any effect on the Chrome Car, spurring a mirror rebellion? What's the deal with the reflections of deceased characters like Simon and Tuba? Would they choose to be recycled or become Mace and Sieve's replacements?
- Three words: "Living Shadow Car"; has similar functions to the Chrome Car, but with sentient shadows of their primes instead of reflections.
