I'm not aware of the Brittany Booker story, so I can't say exactly who she is. She could be a student with a great academic achievement story, or a young professional who overcame challenges in her career. There are so many possibilities without more information about this story.
One common theme is his relationships. It could be romantic relationships with other characters in the story's universe. Another theme is his struggle with his own identity, which often makes for an interesting read.
Another theme is his struggle with his identity. Given his character's backstory, fanfic might delve into how he comes to terms with who he is, whether it's related to his powers or his place in the story's world. This can involve internal conflicts and self - discovery.
I'm not sure specifically as I haven't read it. It could be about a character named Harmony Raines having some sort of extraordinary adventure in a fictional world full of magic, mystery or strange creatures.
Brittany is the main character in the story. She is the one who decides to run a marathon, which sets off the whole plot of her journey of self - improvement and discovery.
One popular type might be those that explore Adrian's backstory more deeply. For example, fanfictions could focus on his early days as a vampire and the challenges he faced. Another aspect could be fanfictions that develop his relationships, like his relationship with the main character in different scenarios. There are also ones that might put him in new and exciting adventures outside the main plot of the Bloodbound series.
The theme of loyalty also comes up a lot. His loyalty to his clan or to certain characters in the Bloodbound world is often explored. Fanfics might show him having to make difficult decisions that test his loyalty, like choosing between his loyalty to a friend and the greater good of his vampire community.