Obviously, Bella and the Joker are the main characters. Bella could be a completely original character created for this fanfiction, or she could be a reimagined version of an existing character from another story. The Joker, of course, is the well - known villain from the Batman universe.
In addition to Bella and the Joker, there might be other supporting characters. For instance, there could be other villains from the Gotham underworld who interact with the Joker and by extension, with Bella. Or perhaps there are some ordinary citizens of Gotham who are affected by the events that unfold due to Bella's and the Joker's actions.
Well, a Bella Swan and Joker fanfiction could be really interesting. It might explore a scenario where Bella, from the 'Twilight' series, somehow gets transported to the chaotic world of the Joker. Maybe she uses her own kind of 'vampire - like' calmness to deal with the Joker's madness.
One common theme is the clash of different worlds. Bella comes from a more supernatural - tinged world in Twilight, and the Joker is from the gritty, crime - filled Gotham. So, the fanfictions often explore how these two disparate worlds collide when the characters meet.
There's also a possibility that some of the more morally grey characters in Gotham, like Catwoman, could be Bella's allies. Catwoman has her own code of ethics, and she might relate to Bella's struggle between good and evil. They could work together in certain situations, especially if there are mutual benefits involved.
The Joker and Batman are the key players. However, in some fanfiction, other characters from the Batman universe might also play important roles, like Harley Quinn who has a close relationship with the Joker, or Commissioner Gordon who is often involved in the Batman - Joker dynamic.
Batman would definitely be a main character. He's the Joker's arch - nemesis, and when the Joker becomes a baby, Batman might be the one who first discovers him. He'd be in a moral dilemma about what to do with this baby version of his greatest enemy.
The main character is always Bella in this type of fanfiction. However, new characters could be introduced as well. For instance, a blind mentor who has learned to live fully with blindness could be added. This character could guide Bella and help her accept her condition. Or there could be a villain who tries to take advantage of Bella's blindness, which would then lead to a conflict where Bella has to use her wits and other strengths to overcome the villain.
There could be Edward. Even if Bella is now immortal, Edward might still play a significant role. He could be either her eternal love or her adversary depending on how the fanfiction is written. Another character could be Alice. Since Alice has her own special abilities, she might be there to help Bella navigate the new world of immortality. For example, she could foresee some of the challenges that Bella will face. Also, Jacob might be a main character. His relationship with Bella, whether it's a friendship or something more complicated, could be further explored in the context of Bella's immortality.
There could be Edward. Maybe he is involved in Bella's life with her psychic powers. He might be curious about her abilities or even try to protect her from the consequences of using those powers.
There could be a female character, Sofia, who is another member of the mafia. She sees Bella as a threat at first, thinking she'll steal her position or the attention of the men in the mafia. But as time goes on, they might form an unlikely alliance. There may also be a young and ambitious mafia underling named Antonio, who is always looking for ways to climb the ranks and his actions often impact Bella's situation in the story.
One common theme is the idea of opposites attracting. Bella and Joker are very different characters, so this theme of how their differences complement each other is often explored.