One common theme is power dynamics. Since Jane has significant power in the Volturi and Bella is a human turned vampire with her own set of abilities, their interactions often revolve around power. Another theme is the struggle between good and evil. The Volturi are often seen as more on the 'evil' side, and Bella represents a kind of 'good', so how they interact with this divide is a theme. Also, there's the theme of forbidden love or attraction, as their relationship is not a typical one in the Twilight universe.
One great piece of jane volturi and bella fanfiction is 'Jane's Obsession'. It explores a different side of Jane's character in relation to Bella. Another one could be 'Bella and the Volturi World' which delves into how Bella might interact more with the Volturi, especially Jane. There's also 'Jane's Redemption in Bella's Eyes' which offers an interesting take on their relationship.
Another plot idea is that Bella is sent to the Volturi as an emissary from the Cullen family for some reason. During her stay, she gets to know Jane better. Jane initially hates Bella for her association with the Cullens, but Bella manages to show Jane a different side of humanity and vampire - human coexistence. This could lead to a change in Jane's view of the world and a shift in the Volturi's policies towards the Cullens.
In the Twilight universe where this fanfiction is based, the Volturi kings are Aro, Caius, and Marcus. They are the leaders of the Volturi, an ancient and powerful coven of vampires.
Aro could be a great addition. Since he is the leader of the Volturi, his presence could add a lot of political intrigue. He might be interested in Bella's unique connection to the Cullens and could either try to use her or be in conflict with Jane over what to do with her.
There could be other vampires that Bella meets during her time as a vampire before the Volturi. For example, some lone vampires who are also trying to stay out of Volturi's radar. They could become her allies or foes depending on their motives.
There is also a possibility that a lone vampire, who has a sense of justice or who has been secretly observing Bella and has grown fond of her, decides to take on the Volturi and rescue her. This vampire could have some special abilities or knowledge that gives them an edge against the powerful Volturi.
Love and friendship are also common themes. Despite the often - dark and power - hungry nature of the Volturi, fanfictions often explore the possibility of Harry and Jane forming a friendship or even a romantic relationship. It's a contrast to the cold and calculating nature of the Volturi world, which makes it all the more interesting.
Definitely. Tumblr is another place to search. Some of the jane volturi and oc fanfiction on Tumblr are really unique. They might incorporate different art forms like fanart along with the written story, giving a more immersive experience. Also, the Tumblr community often has discussions about these fanfictions which can help you discover new and great ones.
Power is a common theme. The Volturi are a very powerful coven, and Bella's relationship with them often involves her dealing with their power. Another theme is loyalty. Bella has to decide where her loyalties lie - with the Cullens or with the Volturi. And of course, love. Whether it's her love for Edward or some new relationships she forms within the Volturi world.