The dead girl might be a symbol of the past that haunts the main character. In a story where the main character is trying to move on from a troubled past, her death could keep pulling him back into that dark place, constantly reminding him of what he has lost or what he has done wrong in the past.
She could be a motivation for the main character. For instance, if the main character is a detective, her death might be the case he has to solve.
Often, the dead girl in a main character story serves multiple purposes. It might be a device to introduce conflict. If the main character was close to her, it could lead to internal conflict within the character, like guilt or a desire for revenge. In a love story, her death could be a heart - breaking event that changes the main character's view on love forever. It can also set the tone for the whole story, making it more solemn or melancholic.
There are several potential causes. Murder is unfortunately a cause in some true stories. Also, self - harm or suicide could be the reason in certain cases. In addition, environmental factors like exposure to toxins or extreme weather conditions in some situations might lead to the death of the girl.
One plotline could be that the girl is on a quest to find out why she is in this state between living and dead. She travels through different realms, from the land of the living to the edges of the afterlife, meeting various characters along the way who either help or hinder her search.
Since we don't know the exact story, it's likely the girl is one of the main characters as she is in the title. She is the one on the train and presumably involved with the situation regarding the dead woman.
Since I don't know the exact 'dead girl story', I can't give the main plot. But generally, it could be about finding out who the girl was and how she died.
She could be a hero, saving the day in the story.
One reason could be to seek justice. If she was wronged or murdered, by telling her life story, she might hope to expose the truth and make sure the perpetrator is punished.
One possible theme could be the struggle between two worlds. The girl is caught between the living and the dead, and she has to face the challenges of belonging to neither completely. Another theme might be acceptance. She has to accept her new - found situation and the things she can see and do.
It might bring a lot of confusion and disbelief. People might question how and why it happened.
The girl, being the monitor, is likely in a position of authority. She may be responsible for maintaining order or ensuring tasks are completed. The two guys could be either students or colleagues, and they might be the ones causing trouble or presenting challenges for the girl to handle.