It could be a new vampire who is jealous of Edward's relationship with Bella. This vampire might be from a far - off place and has heard about the Cullens and Bella. They decide to kidnap Bella to make Edward suffer. Another possible antagonist could be a human who has a grudge against the Cullens. Since Bella is associated with them, they target her. For example, a human whose family was attacked by a vampire in the past and blames the Cullens for not preventing it. They think that by kidnapping Bella, they can get back at the Cullens.
In some fanfictions, Bella might be kidnapped by a new vampire species that is trying to understand the relationship between humans and vampires. They see Bella as an important specimen since she is so deeply involved with the Cullens. So, they take her away to run tests on her, not with any malicious intent initially but more out of scientific curiosity. Another idea is that a witch or a magical being in the Twilight universe kidnaps Bella. They might believe that Bella's connection to the vampires has some sort of magical significance that they can use for their own gain. For instance, they could think that her blood has some special property that can enhance their magic. A more simple plot could be that a human who is jealous of Bella's relationship with Edward kidnaps her. This human might be someone who has a crush on Edward and thinks that by getting rid of Bella, they can have a chance with him.
It could be a rogue vampire who wants Bella for her unique blood. There are many vampires in the Twilight world who might be tempted by her smell. Another potential kidnapper could be a vengeful werewolf who blames Bella for something, perhaps for the way the vampires and werewolves' relationship has changed. It might also be a human who has somehow found out about the vampire world and thinks they can use Bella to gain power or knowledge.
It could be a rogue vampire. Maybe a vampire who has a grudge against the Cullens and figures that taking Bella is the best way to get back at them. This vampire might be acting alone, thinking that he or she can use Bella to bargain with the Cullens for something they have.
Another possibility is a werewolf who has lost control or has a different agenda. In the Twilight universe, the werewolves and vampires have a tenuous relationship, and a werewolf kidnapping Bella could add a whole new layer of conflict. It could be a werewolf who doesn't trust Bella's relationship with the vampires and thinks she's a threat to their pack in some way.
Well, one common plot twist could be that the kidnapper is actually a long - lost relative of Bella's with a hidden agenda. Another might be that the kidnapping was a set - up by a jealous vampire from another coven who wants Edward for themselves. And sometimes, it could turn out that Bella has some sort of hidden power that the kidnapper is trying to either use or suppress.
In some of these fanfictions, one plot could be that Bella's kidnapping is part of a scheme by a new vampire coven that wants to use her as bait to lure Edward. They might think that by having Bella, they can draw out Edward and his family and then overpower them to take over their territory.
One common plot twist could be that the kidnapper is actually a character who was thought to be dead in the original Twilight series. This sudden revelation can completely change the direction of the story.
In 'Kidnapped Love' Twilight fanfiction, it could be that a vampire kidnaps a human for some dark or misunderstood reasons. This could lead to a complex exploration of the vampire - human relationship. The kidnapped person might initially be terrified but then start to understand the kidnapper's motives, which could be related to love in some convoluted way.
Her father, Charlie, might try to rescue her. He loves Bella deeply and would be very worried when she goes missing. He could start investigating and find out that the Cullens are involved.