Maybe it's a side character from the original Twilight books that the writer decides to give more depth to. Like one of the lesser - known vampires in the Volturi coven who has a secret past and motives that are explored in the fanfic.
It's possible that the main character is a time - traveler who accidentally ends up in the Twilight universe. They would have to navigate the strange world of vampires and werewolves while also trying to find a way back home, all while changing the course of the Twilight story in unexpected ways.
There's also a possibility that it could be a self - insert of the author. In this case, the author imagines themselves living in the Twilight world and having the ability to redo certain situations, which would make them the main character driving the new narrative in this fanfic.
Maybe it's Bella. In this fanfic, the focus could be on Bella's relationship with the 'brown - eyed beauty' and how they interact. They could become best friends or rivals.
Perhaps it's a story that focuses on the afterlife of a character from Twilight. Like, what if a vampire or a human who died in the original story gets a second chance at life in a different form? It could explore how they deal with their new existence and the relationships they form or re - form in this new state.
Edward could also be the main character. He has his vampire senses which could help him analyze the bloody fingerprints in ways humans can't. He might be on a mission to protect Bella and the rest of his family from whatever danger the fingerprints signify. Maybe he suspects that it's a new threat from a nomadic vampire group and he has to use his skills to track them down.
Arya Stark from 'Fire and Ice' could be a great main character in a 'Fire and Ice Twilight Fanfic'. She has the skills of a trained assassin and a strong will. In the fanfic, she could find herself in the world of 'Twilight' and use her skills to navigate the dangerous world of vampires and werewolves. Maybe she would form an alliance with the Cullens or the werewolf pack and help them in their battles.
There could be a young unicorn named Starlight. He might be a brilliant but overconfident student who Twilight has to guide. Another character could be a pegasus named Rainbow, who is always getting into trouble and Twilight has to keep in line.
It could be a woman who was once an ordinary Twilight fan but then became a trophy wife. So she brings her Twilight obsession into her new life. She might be someone who is constantly trying to balance her love for Twilight with her new - found status as a trophy wife. For instance, she may try to incorporate Twilight - related items or themes into her luxurious lifestyle.
I'm not entirely sure specifically as there are many 'Twilight' fanfics. Generally, a 'Twilight My Immortal' fanfic might be about the 'Twilight' universe, perhaps exploring different relationships between the characters like Bella and Edward in new and creative ways. It could also introduce new plot elements or expand on the lore of the vampires and werewolves in the 'Twilight' series.
It could be a new girl in Forks who just moved there. She has this pink fluffy pencil case that she got from her grandmother. And she gets involved in the Twilight world because of the strange things that start to happen with the pencil case.
It could be Ana, the main character from 'Real Women Have Curves'. Imagine her being transported into the 'Twilight' world and having to deal with vampires and werewolves while still holding on to her strong - willed and body - positive self.