In many fanfictions, Red X could be Robin. Maybe he has some secret motives or a hidden side that leads him to take on the Red X persona. It could be a way for him to operate outside the normal constraints of the Teen Titans while still being involved in the action.
Well, obviously Red and Yellow are the main characters. Red is often depicted as a bold and adventurous character, while Yellow might be more of a gentle and kind - hearted one. They play off each other in the story.
Other minor characters from the Teen Titans universe might also make an appearance. Maybe some of the villains that are associated with Red X could be there in the background, influencing his actions towards Starfire. Or some of the civilians that the Teen Titans protect, who could be caught in the crossfire of this struggle between Starfire and Red X, and their presence could add more complexity to the story.
It's hard to say who the 'best' writers are as it depends on personal taste. However, some well - known writers in the fanfiction community might be worth checking out. Look for those who have a lot of positive reviews and comments on their stories. You can start by searching on popular fanfiction websites and sorting by the highest rated Red Hood x Batgirl fics.
Red and Blue themselves are often popular characters. Their rivalry and different approaches to Pokemon training can make for great stories. Also, Professor Oak is a well - liked character as he often plays an important role in the fanfic, like giving advice or providing new Pokemon to trainers.
A lot of fanfics might focus on a mission or adventure that they go on together. This gives the opportunity for them to bond and develop feelings for each other in the face of danger.
You can try searching on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfics from various fandoms, and you might be able to find some great Starfire x Red fanfics there by using the search function.