A common theme is friendship. Despite their differences, Bella and Leah often form an unexpected friendship in many fanfics. Another theme is self - discovery. Both characters go through a process of understanding themselves better in relation to each other.
Another theme is redemption. Leah, who has a rather complex and often misunderstood character, might be shown finding redemption or a new sense of purpose through her relationship with Bella. This could involve her coming to terms with her own issues and growing as a person.
Perhaps Bella jumps on Leah in a moment of fear. For example, if there's a sudden danger and Bella sees Leah as a source of protection, so she jumps on her instinctively. This could then lead to a story of their growing bond as they face the threat together.
One popular 'bella leah fanfic' is 'Leah's Redemption'. It delves into Leah's character development in a unique way. Another one could be 'Bella and Leah: An Unlikely Friendship' which explores an interesting relationship between the two. There's also 'Leah's Perspective on Bella' that gives a different take on their interactions.
I'm not sure which specific 'bella lunged at leah fanfic' there are. You could try searching on fanfic websites like Archive of Our Own or FanFiction.net.
At first, their friendship might start out tentatively. They have had their differences in the original Twilight story. But as the fanfiction progresses, they start to understand each other better. Leah might open up more about her own insecurities and past traumas, and Bella, in turn, shares her own fears about being involved with vampires.
You can try some popular fanfiction websites like Archive of Our Own (AO3). There are a large number of fanfics about various pairings, including bella x leah. Just search for the relevant tags on the site.
I'm sorry, I don't have specific 'bella jumped on leah fanfic' stories to recommend directly. You could try searching on fanfic websites like Archive of Our Own. There might be a lot of creative works there related to these characters.
One common theme is friendship. Since they start off with a bit of animosity in the original story, fanfictions often explore how they can become friends.