Perhaps in the fanfiction, there's a misunderstanding within the werewolf pack. Some members believe Bella is a threat to their territory or secrets. They attack her without fully understanding the situation, and unfortunately, she is beaten to death. This could lead to a huge rift between the vampires and the werewolves, as Edward and his family would seek justice for Bella.
It could be that a group of rogue vampires, not following the Volturi's rules, come across Bella. They see her as an easy target, being a human among vampires. They attack her brutally, beating her to death. This would cause a stir in the vampire world, as Bella was under the protection of the Cullens, and might even draw the Volturi's attention to the situation in Forks.
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.
Edward would be completely devastated. He would likely go into a blind rage and seek out whoever was responsible for Bella's death. His love for her was so intense that he would stop at nothing to avenge her.
Perhaps in the fanfic, Voldemort has found a way to nullify Harry's magic for a short time. Without his magic, Harry is just a normal boy and Voldemort takes this opportunity to beat him to death. It could also be that Voldemort has an unexpected accomplice who helps him corner Harry, leading to Harry's demise.
One interesting plot could be Bella developing a new power while living with the Cullens. For example, she might gain the ability to communicate with animals like some of the other vampires. This would add a new dynamic to her relationship with the Cullens and also pose new challenges and adventures as they try to keep it a secret from the outside world.
There could be a plot where a character's death in the Twilight fanfiction sets off a chain of events that no one expected. Maybe their death reveals a long - held secret in the vampire or werewolf community, and the other characters have to deal with the consequences while also grappling with the loss. This would add an element of mystery and drama to the fanfiction.
Perhaps a plot where they embark on a journey to discover the origin of their Futa existence within the Twilight universe. This could involve meeting ancient vampires or other supernatural beings who hold the key to their transformation. They would face many challenges and learn more about themselves along the way.
One interesting plot could be where Jacob and Bella go on a secret adventure in the forest together. They discover a hidden part of the forest that has a special meaning to the werewolves. It could involve them facing some small challenges like crossing a rapid stream or finding their way back when they get lost.
One interesting plot could be Bella having to teach vampire children about the human world in a way that they can understand without revealing too much. For example, she might tell them stories of holidays like Christmas, which are so different from their vampiric existence.
There could be a plot where Bella has a premonition about a danger that's going to befall the wolf pack. She then tries to convince them of the impending threat, but they are hesitant to believe her at first. Through her determination and the evidence she manages to gather, she eventually gets the pack to take her seriously and they all work together to face the danger.
One interesting plot could be Bella's struggle to control her new vampire powers. She might face difficulties in adjusting to her heightened senses, like being overwhelmed by the smell of blood. Another plot could involve her relationship with Edward. Since she's now a vampire, their dynamic might change, and they could face new challenges together.