Well, Bullet Train isn't a manga. It could be a novel adaptation or a completely original concept for a movie or something else. But in the realm of manga, it doesn't exist.
One popular 'bullet train fanfic' could be about the adventures of the passengers on a bullet train during a special event, like a mysterious stop at an uncharted station. Another might focus on the relationship between the train staff and how they handle various situations on the bullet train.
One common theme is character backstories. Writers often explore the pasts of the characters from the Bullet Train movie, like Ladybug's early days as an assassin. Another theme is alternative universes, where the events of the movie take a different turn, for example, if the characters had different allegiances.
Fanfiction.net is also a great place. There are many talented writers who contribute to the bullet train fanfiction there. However, the quality may vary, so you might need to read a few summaries or reviews before choosing a story.
I'm not sure specifically which 'bullet train novel' you are referring to. There could be many novels related to bullet trains. It might be about a story that takes place on a bullet train, perhaps involving mystery, adventure, or the lives of the passengers.
Bullet Train is not based on a true story. It's a work of imagination crafted by the writers to offer a thrilling and engaging narrative. The plot and characters are invented to captivate the audience.
First, think about the setting. Decide if it's a modern - day bullet train or one in a fictional, perhaps futuristic world. Then, create your characters. They could be passengers with different backgrounds and motives. For example, a detective on the train solving a mystery.