Simon's character can be developed by exploring his backstory. If he has a troubled past, it can be revealed gradually as he gets closer to Bella. Also, his relationship with Bella can make him more empathetic or more guarded depending on how their interactions play out. For example, if Bella is initially suspicious of him, he might become more defensive in his behavior.
You can develop their characters through their shared experiences. Let's say they go on a journey together to find a cure for a new disease that is affecting both humans and supernatural beings in Forks. During this journey, Bella can become more courageous as she faces new challenges, and Simon can show his loyalty and determination to protect Bella and find the cure.
To develop Bella in this fanfiction, she could be given a mentor. Maybe an old witch who has been watching over her. With the mentor's help, she can learn about the history of doppelgangers in the witch world and how to control her powers. She can also struggle with the morality of using her powers, like whether she should use them to get revenge on those who have wronged her in the past.
Bella Swan's character could be developed by having her explore different aspects of herself. In the context of Greek gods, she might discover a more passionate side of herself, like the passion associated with the Greek concept of eros. This could make her more confident and change her relationships. She could also be developed through her experiences with the Greek gods' powers. If she gets a taste of Athena's wisdom, she could use it to solve problems in Forks that she couldn't before. This would make her a more respected and important figure, not just among the Twilight characters but also among the Greek gods she encounters.
A well - crafted plot that combines the two different universes is key. It could involve how their different supernatural worlds interact, like the vampires in 'Twilight' and the demons in 'Shadowhunters'. Maybe a situation where they have to use their unique abilities to solve a problem that spans both worlds.
A plot could revolve around Simon being a long - lost relative of Bella's. He shows up in Forks and his presence disrupts Bella's relationship with Edward. Simon has his own secrets about the supernatural world which Bella gradually uncovers, and she has to decide between the two different worlds she's now a part of.
One way is to explore the backstory of Petrova more deeply. If Bella is a fan, then showing what makes Petrova so fascinating to her through detailed backstories would be great.
One way the story could be developed is by having Bella be a secret Mikaelson fan in the Twilight universe. Maybe she discovers a hidden book about the Mikaelsons in the Forks library. This could lead to her having strange dreams about them and it might even influence her relationship with Edward. For example, she could start comparing Edward's vampire nature to that of the Mikaelsons.
It depends on the specific fanfiction. Some fanfictions focus more on action or other plot elements rather than fully developing their relationship. However, in the ones that do, it can be a really interesting and complex relationship with a lot of emotional depth.
One popular Bella Swan and Simon Lewis fanfiction is 'Unexpected Alliances'. It explores a unique scenario where Bella and Simon team up against a common supernatural threat in a world that combines elements from their respective fictional universes. It has great character development and an engaging plot.
Alice Cullen can be a very popular character. Since she can see the future, in a 'reborn as bella swan' scenario, her interactions with Bella could be really different. Maybe she tries to guide Bella in a new way based on her visions. Also, Carlisle Cullen is popular. His father - figure role towards Bella might be explored further in these fanfictions.
Edward Cullen would likely be a main character. His reaction to Bella's situation, whether it's concern for her well - being or struggle with his vampiric instincts around her period blood, could be a major part of the story.