One common theme could be the struggle for dominance between the mates. Since it's possessive, there might be a lot of tension regarding who has more control or claim over the other.
I'm not sure specifically which 'bella and jane mate possessive fanfiction' to recommend. You could try searching on popular fanfiction websites like Archive of Our Own or FanFiction.net. They have a wide variety of fanfictions and you might find the ones related to this topic there.
The theme of the supernatural bond between them is also common. Given that they are part of the Twilight world with vampires and mates, their possessive relationship is often tied to this supernatural element. Their bond is not just a normal romantic relationship but something deeper and more powerful, which is a major theme in these fanfictions. It can lead to some really interesting plotlines where their supernatural bond either strengthens or is tested due to Jasper's possessiveness.
There could be characters from the original stories that Bella and Jane come from. For Bella, characters like Edward or Jacob might still play a role, perhaps in the form of her past relationships that now create some sort of complication in her new relationship with Jane. From Jane's side, other Volturi members could be involved, like Aro or Caius, who might have opinions on Jane's new mate.
Well, it could be about how Bella and Jane overcome the differences between their two characters. Maybe they start off as enemies since they are from different sides in the original story, but then gradually find common ground and develop a strong bond as mates.
There's also 'Bella and Jasper: A Possessive Bond'. In this fanfiction, it focuses on the early stages of their relationship where Jasper's possessive instincts start to surface. It's interesting as it shows how Bella reacts to this new aspect of Jasper's personality and how they navigate through it together. It also has some great character development for both of them.
It could start with Bella realizing her possessive feelings towards Alice's mate. Maybe it begins with a chance encounter where she sees them together and something inside her stirs.
Well, 'His Werewolf Mate's Claim' is also a wonderful one. The story delves deep into the concept of a possessive werewolf mate. The werewolf's possessiveness is intertwined with his loyalty and the cultural aspects of the werewolf pack. It's a long - form story that really takes you on a journey through their relationship, from the initial meeting to the final claiming of the mate.
I'm not sure of a specific one off - hand. But you can start by looking on popular fanfiction websites like Archive of Our Own. Just search for 'Bella Swan sister Jane mate' and you'll likely find a variety of stories with different takes on the concept.
One interesting aspect could be the exploration of complex relationships. Bella being possessive of Alice's mate might lead to intense emotional drama. It could also show how the characters handle loyalty and jealousy in a unique supernatural setting.