A more complex fanfiction could involve a crossover of the two universes' viruses. The virus in Z Nation and the vampire virus in Twilight somehow interact. Bella, being in the middle of it, has to figure out how to stop a new, more dangerous threat that emerges from the combination of these two 'viruses'.
One idea could be a crossover where Naruto characters end up in the Z Nation world. For example, Naruto with his shadow clone jutsu could be really useful against the zombies. He could send out clones to distract the zombies while the group tries to find a safe place.
There could be many interesting scenarios in such a fanfiction. Maybe 10k, with his survival skills from Z Nation, ends up in the Twilight universe and meets Bella Swan. He could help her in a different way from the Cullens, perhaps using his combat skills against some new threats in Forks.
Another concept could be that a character from Sons of Anarchy has a vision or encounter similar to Bella's transformation in Twilight. This could lead to a whole new set of challenges and changes within the Sons of Anarchy universe. It might also bring a new dynamic to the relationships within the gang as they try to figure out what's happening to their comrade.
She would be more hardened. In the Twilight world, she was mainly dealing with the supernatural in a relatively civilized setting. In Z Nation, she'd have to be tougher to survive the zombie - filled chaos. So she might be less naive and more street - smart.
They could be friends. 10k, having seen so much death and chaos in Z Nation, might find Bella's somewhat normal life (despite the vampires and werewolves) refreshing. And Bella could be interested in 10k's tales of survival.
A fanfiction could explore 10k's backstory more in - depth. Maybe he had a family before the apocalypse that he is constantly reminded of during his travels. This could add a whole new emotional layer to his character.
Perhaps Bella Swan could be a time - traveler in a fanfiction. She travels back in time to the era of Harry Potter and gets involved in the fight against Voldemort. She could use her skills of self - preservation and her knowledge of the future (from her Twilight world) to help the Order of the Phoenix. For example, she might know some strategies for dealing with dark forces that could be adapted to the wizarding world.
One idea could be to focus on Bella's inner thoughts during the birth. Maybe she reflects on her journey from a normal girl to a vampire's mate and how this new life she's bringing into the world will fit into their supernatural existence. For example, she might worry about the baby's safety in a world full of vampires and werewolves.
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.
Well, in 'z nation oc fanfiction', you can find stories where original characters form their own groups and have unique survival strategies. They might team up with some of the known characters from the series in unexpected ways. One story could be about an OC who is a master of disguise and uses this skill to infiltrate zombie - infested areas to gather supplies.