It's fiction. The story and characters in 'The Splendid and the Vile' are invented to entertain and engage the readers rather than being based on real-life happenings.
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.