An old werewolf who has decided to retire from the pack life and goes on a trip to all the places that were important to the werewolves in the Twilight story. Along the way, they might run into some vampires and have to face old prejudices and form new alliances.
Well, they could go on a trip around the world to gather ancient artifacts that have the power to either strengthen or destroy the vampire - werewolf peace in Forks. This would involve lots of action, mystery, and interactions with different characters from the Twilight world.
Well, in Twilight fanfiction, the role of a lifetime might be a re - imagining of an existing role. Take Edward for example. In some fanfictions, his role as a vampire might be re - defined to be more of a protector not just of Bella, but of the entire town. It could also be about a character taking on a role that challenges their nature. Like Rosalie having to play the role of a peacemaker, which goes against her often - prickly personality in the original story.
Bella Swan is a very likely character. Since she has such a strong connection to Forks, which is her home in the Twilight world. Her journey home could be filled with thoughts of Edward and the vampires she has come to know.
One way to create the role of a lifetime in Twilight fanfiction is by focusing on a character's backstory. If you're creating a new character, give them a rich backstory that ties into the Twilight lore. For instance, a vampire who was turned during the Roman Empire and has a vendetta against the Volturi. Their role could be to expose the Volturi's secrets and change the power structure in the Twilight world. You also need to make sure the role has an impact on the main characters and the overall plot.
Perhaps it's about one of the werewolves going back to their reservation. They might be reflecting on how their life has changed since the appearance of the vampires in the area. For example, Jacob could be on a trip home and thinking about his complex relationship with Bella and his pack.
It could be a new character, like a young girl who has just moved to Forks and discovers she has psychic powers. She then gets caught up in the existing drama of the twilight world.
It could be someone completely new. A character that the author creates to disrupt the status quo in the Twilight universe. This new character might have unique powers or abilities that change the course of the story.
Since it's a fanfiction about a 'perfect stranger', it's likely that the main character is this stranger. But without reading it, it's hard to say more about who they are exactly.
Edward Cullen could be a great main character. Since he is already a part of the Cullen family who loves baseball, he could be the one to hit a crucial home run. Maybe this home run is what saves Bella from some sort of danger during a baseball - related event. For example, the Volturi might be there to cause trouble during a game, and Edward's home run distracts them long enough for Bella to get to safety.
A new character could be introduced as the main character. This character could move to Forks and be unaware of the supernatural world there. Their arrival could trigger a series of events that force the existing Twilight characters to have a fresh start in how they deal with their secrets and relationships.