A human friend of Bella's could be the main character. Someone who is not fully aware of the vampire - werewolf world at first. When they find the crown at Christmas, they are drawn into this hidden world. They might be the key to uniting the different factions because of their outsider perspective and the power of the crown they possess.
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.
Love and sacrifice are also common themes. Just like in the original Twilight series, in 'A Crown for Christmas' Twilight fanfiction, characters might have to make difficult choices between their love for someone and their duties or the safety of others.
It could be a new character entirely. Maybe a young vampire who was turned recently and is still adjusting to the 'alive inside' state of being undead. This character could struggle with the morality of being a vampire while also trying to fit into the Twilight world's complex social structure.
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.
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.
Another option could be Jacob. As a werewolf, he has a connection to the spiritual side of the Twilight world. He might be the one to discover the hauntings first and have to figure out how to deal with them, especially if they pose a threat to his pack or the people he cares about in Forks.
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.
A young vampire who was recently turned against their will. They are lonely because they miss their human life and family, and they don't fit in with the other vampires yet. They are constantly haunted by nightmares of their transformation and the life they've lost.
Alice could also be the main character. Given her ability to see the future, she might be the first to sense the impending doom of the bitter sun rising. She could be using her visions to guide the other characters, trying to change the future and prevent the worst - case scenarios that the new sun could bring. Her quick thinking and ability to adapt would make her a great protagonist in this fanfiction.
It could be Bella. She often finds herself in the middle of the vampire - werewolf drama in the original Twilight series. So in 'getting back to myself', she might be trying to find her true self again after all the chaos and changes she has been through. Maybe she wants to go back to the simple girl she was before getting involved with Edward and the vampire world.