It's also possible that some of the werewolves who are not as accepting of change could view Bella's new mermaid form as something abnormal and a potential danger to their pack. So they could act as antagonists in the story, causing trouble for Bella as she tries to adjust to her new life.
Perhaps the Volturi could still be the main antagonists. Even though Bella is now a mermaid, the Volturi's strict laws about the supernatural world might still put her in danger. They could see her mermaid nature as a threat to their control.
One common theme is the exploration of Bella's identity. Since she's a mermaid in these fanfictions, it often looks at how she reconciles her new mermaid self with her human side. Another theme is the relationship changes. Her being a mermaid can greatly impact her relationships with Edward, Jacob and others.
Well, in some Twilight fanfiction involving a mermaid Bella, she is often adapted to have unique abilities. For example, her mermaid nature might give her enhanced swimming skills that are far beyond normal vampires or humans in the Twilight universe. This could also lead to new plotlines where she has to hide her true form from the other characters.
Well, one interesting aspect could be the unique combination of the mermaid element with the Twilight universe. It might bring a fresh perspective to the Bella character, perhaps giving her new powers and abilities as a mermaid that could change her relationships within the Twilight story. For example, her interactions with the vampires and werewolves could be completely different.
One common plot twist is that Bella's mermaid identity is revealed in a very unexpected way. Maybe during a swim with the Cullens, she suddenly transforms, shocking everyone. Another is that her mermaid powers are somehow connected to the Volturi's plans, adding a new layer of danger.
One popular 'bella mermaid twilight fanfiction' is 'Bella the Mermaid Princess in Twilight'. It gives a really interesting take on Bella as a mermaid in the Twilight universe. The author does a great job of mixing the mermaid lore with the existing Twilight elements.
There could be a friend of Bella's, like a human friend who starts to suspect that something is different about Bella. This character could add an interesting dynamic as they try to figure out Bella's secret and support her at the same time.
It could be other werewolves who oppose the union of a human and a werewolf. They might see the pregnancy as a threat to the purity of the werewolf bloodline or something against their traditional beliefs.
In some Bella and Jasper military fanfictions, the main antagonists could be rival military groups. These groups might have different ideologies or goals and be in direct competition or conflict with Bella and Jasper's unit. For example, they could be fighting over territory or resources. Another type of antagonist could be a power - hungry military leader within their own ranks who is willing to sacrifice the well - being of the soldiers for personal gain.
Often, the Volturi can be antagonists. They might not approve of Jasper and Bella's relationship for some reason, like they think it goes against vampire laws or traditions. Another possible antagonist could be a rogue vampire who has a vendetta against the Cullens and sees Jasper and Bella's relationship as a way to get to them.
In some cases, a powerful and rogue vampire who has his own agenda could be the main antagonist. This vampire might be after Bella for some special ability she has or he could have a vendetta against Rosalie. He would constantly be causing trouble for them, trying to disrupt their lives and relationships within the Cullen family.