Well, in kurapika and neon fanfiction, a common theme could be the contrast in their worlds. Kurapika is from a tragic background with his clan's destruction driving him. Neon, on the other hand, is a part of a wealthy and powerful family. Fanfic writers may play with the idea of how these two from such different walks of life come to understand each other. Maybe Kurapika sees in Neon a glimmer of innocence that he wants to protect, or Neon could be intrigued by Kurapika's mystery and strength.
There's no way to really tell if it's common specifically for someone named Jojo. However, in general, reading fanfiction is a popular activity among fans of many different franchises. The Jojo series has a large and dedicated fan base, so it's likely that there are fans named Jojo who partake in reading fanfiction, but we can't say for sure how common it is without more data.
Perhaps this Jojo is interested in exploring different interpretations and stories within the Jojo universe that fans have come up with. Fanfiction often takes the existing characters, settings, etc. from the original Jojo series and creates new and unique storylines. So, this Jojo might be a big fan of the series and wants to see what other fans have imagined.