One possible fanfiction plot could be that Deathstroke kidnaps Robin to use him as bait for Batman. He wants to lure Batman into a trap and finally defeat him. Robin, being the resourceful sidekick, leaves behind small clues for Batman to find him, adding an element of mystery and suspense to the story.
To create a believable relationship, start with their fundamental differences. Robin is a hero, and Deathstroke is a villain. They could be initially at odds, constantly trying to outwit each other. But then, introduce some common ground, like a shared enemy or a mutual respect for each other's combat skills. This can slowly build a complex relationship.
Robin could use his intelligence to analyze Deathstroke's lair and find a weakness in its security system. He might notice a pattern in the guards' patrols or a flaw in the locking mechanisms. Then, he could use his acrobatic skills to create a distraction and slip away unnoticed.
Nightwing could also be a likely savior. He was once Robin himself and has a strong bond with the current Robin. He might take it upon himself to rescue Robin, using his own unique fighting style and experience to outwit the Joker. Plus, he has his own network of contacts in Gotham that could help in the search.
In one scenario, the Joker might kidnap Robin to taunt Batman. He could hold Robin in a secret, elaborately booby - trapped lair. Robin, being the resourceful sidekick, would try to find ways to escape and leave clues for Batman. The Joker would then play mind games with both Robin and Batman through recorded messages and false leads.
The plot might go like this. Slade kidnaps Robin in a very stealthy way. He takes Robin to an abandoned building. There, he tries to indoctrinate Robin into his way of thinking. He could be telling Robin that Batman is using him and that he can offer Robin more power. However, Robin stays true to his beliefs. Meanwhile, Batman is on a frantic search for Robin, following every lead, and the Bat - family is also on high alert. Robin is constantly looking for an opportunity to turn the tables on Slade and escape.
Well, first off, Deathstroke is a formidable foe. If he kidnaps Robin, he might try to extract information from him about Batman's weaknesses. Robin, being loyal, would of course resist. It could lead to a physical and mental battle between the two.
One possible plot twist could be that Robin has been secretly trained in a new combat technique that he uses to outwit Deathstroke when Deathstroke least expects it. Maybe he pretends to be more injured or helpless than he really is, and then strikes back at a crucial moment.
One idea could be that Robin is on a solo mission and Deathstroke is hired to stop him. Robin has to use his wits and agility to outmaneuver Deathstroke's superior strength and experience. Another could be that Deathstroke, for some reason, decides to train Robin secretly, leading to a complex relationship between the two where Robin is conflicted about learning from an enemy.