The OC might be more assertive than Bella. Bella was often very passive in the original story, especially when it came to her relationships. The OC could be the type to take charge and make decisions more quickly, not waiting for others to lead the way.
The OC could be more outgoing and sociable compared to Bella. Bella was a bit of an introvert, but the OC might thrive in social situations. This would change how they interact with the other characters in Forks. Instead of being the quiet new girl, the OC could be the life of the party, which would attract different kinds of attention from the vampires and werewolves. It would also change the way they form relationships, as they would be more likely to make friends and enemies more quickly.
Maybe the OC has some hidden powers or knowledge from their past life. For example, they could know a way to defeat the Volturi that no one else in the Twilight world is aware of. This would lead to a whole new storyline where the OC has to convince others of this knowledge and face the challenges that come with it.
In the original story, Bella doesn't really have any powers until she becomes a vampire. But in fanfic, her powers can be very different. For instance, she could have pre - transformation powers like the ability to sense danger from a distance, which is not in the original at all.
If an OC is reincarnated in DxD fanfiction, their personality could be affected in various ways. They might become more assertive due to the dangerous environment. For example, having to face devils and angels constantly could make them more confident in standing up for themselves.
She might become more protective. As Silas's sister, she would have a natural inclination to safeguard him, which could make her more assertive.
Edward could be one of her allies. He could use his vampire abilities such as super - speed and strength to assist Bella in dangerous situations. His centuries - old knowledge could also prove invaluable in understanding the motives and actions of the CIA's enemies. Another ally could be Jacob. His shape - shifting abilities would give the team an extra edge in combat or in covert operations. He could also use his connection to the werewolf pack to gather information from areas that the CIA might not have easy access to.
One common theme is friendship. The OC often forms a unique bond with Bella, either helping her through tough times or just being a great friend. Another theme is the exploration of the supernatural world. Since the Twilight series has a lot of supernatural elements, the OC usually gets involved in that aspect too, like dealing with vampires and werewolves.
She would likely become more confident. Knowing she is the daughter of Hades, a powerful god, would give her a sense of self - worth that she might not have had before. For example, instead of being the damsel in distress in her relationship with Edward, she could be an equal partner, using her powers to protect him and his family if needed.
The male Bella Swan in the fanfic might face different expectations from society within the story. In the original, Bella had to deal with being the new girl in town. As a male, he might have to deal with different social hierarchies, like being part of male groups or facing different forms of competition. This would also impact the overall plot.
In some fanfictions, Bella's character might become more confident. As an immortal, she no longer has the same fears of mortality. For example, she could be more fearless in facing dangerous situations.
Bella could develop a stronger sense of survival. In the face of the mob's threat, she has to constantly be on the lookout for danger. This would make her more aware of her surroundings and better at finding ways to stay alive. For instance, she might learn how to hide, find safe places to stay, and avoid being detected. As she overcomes various challenges during her escape, she may also gain more confidence in her abilities. Initially, she might be very scared and unsure, but as she manages to evade the mob's pursuit, she realizes that she is capable of much more than she thought.