Well, it could start with Red X having some ulterior motive like using Starfire to get to the Teen Titans. Maybe he plans to ransom her or use her powers for his own gain. He might keep her in a hidden lair and Starfire would be trying to escape while also trying to figure out what Red X really wants.
In a 'Starfire kidnapped by Red X' fanfiction, the plot might involve Red X being hired by an unknown villain to kidnap Starfire. Red X could be conflicted during the kidnapping as he might have some feelings for Starfire that he doesn't want to admit. Starfire, on the other hand, would be using her alien strength and powers to try and break free from whatever restraints Red X has put on her.
The story could go like this. Red X sees Starfire as a key to getting a powerful artifact that the Teen Titans are protecting. So he kidnaps her. Starfire is initially shocked and scared but then she realizes she has to be strong. She tries to reason with Red X, but he is stubborn. Meanwhile, the Teen Titans are searching for her, and Red X has to keep her hidden while also fending off other villains who might want to steal Starfire from him for their own purposes.
Obviously, Red X would be the main antagonist as he is the one doing the kidnapping. But there could also be other antagonists in the background. For example, if Red X was working for someone else, that person could also be an antagonist. Maybe a powerful intergalactic criminal who wants Starfire's powers for his evil plans.
One possibility could be that Red X is under some sort of mind control and is made to target Starfire. He binds her tightly as part of a plan to hold her hostage in order to get something from the Teen Titans. Maybe he wants some powerful artifact that the Titans are protecting and he thinks Starfire is the key to getting it.
One possible motive could be to use her as a bargaining chip. Maybe against the other Teen Titans, like Robin or Beast Boy. Red X might want something in return for her safe release.
One possible plot twist could be that Red X has a hidden agenda that's not actually malicious towards Robin. Maybe he's trying to protect Robin from a greater threat that the Teen Titans are unaware of. For example, there could be a new super - villain in the city who is targeting the Titans, and Red X believes that by taking Robin, he can keep him safe until the danger passes.
It could be about an adventure where Red and Sticky have to tie up Starfire for some unexpected reason in the context of a fan - created story. Maybe they're trying to protect her from a greater threat by restraining her temporarily.
Well, it could be that a crazy superfan who is obsessed with Monsta X decides to kidnap them to have them all to herself. She might keep them in a secret location and try to make them perform just for her. Then the members of Monsta X would have to figure out a way to escape and also deal with this deranged fan.
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.
The difference in their moral compasses. Red X is more likely to cross ethical lines. Starfire, with her strong sense of right and wrong, would find it hard to be under his control in his grip, as it would go against her principles.
The red x adhesive could be a key element in a time - travel fanfiction involving Starfire. It might be something that was created in the future and accidentally sent back in time. Starfire discovers it and tries to figure out its purpose. Along the way, she might meet different versions of herself or other characters, all while dealing with the strange properties of the adhesive.
Well, often there could be elements of conflict between Starfire and the Red X goo. Maybe the goo has some sort of strange power that affects Starfire physically or mentally. For example, it could be weakening her powers or causing her to have strange visions. Another common plot element might be Starfire's attempts to break free from the goo's influence. This could involve her using her own strength, both physical and mental, or seeking help from her friends in the Teen Titans.