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.
One great Red X and Starfire fanfic could be a story where Red X is initially a villain but slowly starts to have a change of heart due to his interactions with Starfire. Their relationship could be filled with tension and mystery as they try to understand each other's motives.
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.
One characteristic is the exploration of their opposing personalities. Red X is more of a anti - hero, while Starfire is a heroic and positive character. Fanfictions may focus on how they clash or find common ground. For example, they could be forced to work together on a mission, and during that time, they start to see each other in a new light. Maybe Red X shows a softer side that Starfire didn't expect, or Starfire's optimism starts to rub off on Red X. Also, the fanfictions might delve into the power dynamics between them, considering their different abilities and how they complement or conflict with each other during battles or other situations.
You can try searching on fanfiction platforms like FanFiction.net or Archive of Our Own. Just use the keywords'red x kidnaps starfire' in their search bars. There might be some great stories out there that match this plot idea.
One common theme is trust. Since Red X is a rather mysterious character, Starfire often has to learn to trust him or not. For example, in many fanfics, they start off as distrustful of each other but gradually build trust as they face challenges together.
Another theme is redemption. Red X is often a character who has room for growth and change. So, many fanfictions involve him trying to make up for his past wrongs and earn the respect of Starfire and Robin.
Another theme could be adventure. They are both characters often involved in action - packed scenarios. Fanfictions might put them on a joint mission where they develop feelings for each other along the way. For example, they might have to battle a new super - villain that threatens their city or world, and in the process, their relationship deepens.