Sokka might be a rescuer. He's Katara's brother and he would stop at nothing to save her. He could use his strategic mind and his trusty boomerang to take on the kidnappers. Another potential rescuer could be Zuko's uncle Iroh. He has great wisdom and his own firebending skills. He might be able to outwit the kidnappers and free Zuko and Katara. There's also the possibility of some unexpected characters from their past coming to their aid, like some of the Freedom Fighters they met earlier in their adventures.
Well, it could be the Order of the White Lotus. They are a powerful and secretive group. They might have learned about Zuko and Katara's kidnapping and decided to intervene. Their members include some very skilled benders and strategists. Additionally, some of the Fire Nation citizens who have come to respect Zuko as their leader might also attempt a rescue. They could see this as an opportunity to prove their loyalty to him and show that the Fire Nation is changing for the better under his rule.
The Blue - Eyes White Dragon could be an unexpected rescuer. In some fanfictions, the powerful card could come to life or have a spiritual connection to the Kaiba family. Also, an undercover detective who has been investigating the Kaiba family's enemies might be the one to rescue Mokuba. This detective could have been on the trail of the kidnappers for a while. And lastly, an old family friend or mentor of the Kaibas could emerge to save Mokuba. This person might have some special knowledge or skills that are crucial for the rescue operation.
It could be Zuko's sister Azula. She might see Katara as a threat to her plans or as a valuable pawn to use against Zuko and the Avatar. Azula is known for her devious and manipulative nature.
His friends, of course. Scott would be one of the most likely rescuers. As Stiles' best friend and a werewolf, he has the strength and loyalty to track Stiles down. Lydia might also be involved. With her banshee powers, she could sense Stiles' distress and lead the others to him. Another possible rescuer could be Derek. He has a lot of experience dealing with dangerous situations and might feel a sense of obligation to save Stiles, especially if he realizes Gerard is involved.
Some fanfictions explore their role in rebuilding the world after the war. Zuko and Katara could be working together to restore balance between the nations. This kind of fanfiction often shows their leadership skills and how they complement each other.
There could also be a mysterious figure, like a vigilante type who has been following their cases and admires their work. This person might step in to rescue them, using their own unique set of skills that the kidnappers didn't anticipate.
In a 'Zuko kidnaps Katara' fanfiction, Zuko could be under the influence of some dark force or an evil advisor. He kidnaps Katara thinking she is the key to unlocking a powerful waterbending technique that he wants to use for his own gain. But Katara is a strong - willed character. She doesn't give in easily and instead tries to turn the situation around by appealing to Zuko's better nature, which he has buried deep inside him.
The Akatsuki could be potential kidnappers. They are always on the lookout for powerful jinchuriki like Naruto to extract the tailed beasts from them. Orochimaru could also be a kidnapper as he is always interested in obtaining powerful bodies and Naruto's strength would be very appealing to him.
Hermione could be a potential rescuer. In a different timeline or scenario, she might stumble upon the abandoned Harry and use her intelligence and knowledge of magic to take care of him. Another could be Hagrid. He has a big heart and a love for all things magical. He might find Harry and take him under his wing, protecting him from any harm. And Sirius Black is also a possibility. Even if he was wrongly imprisoned, if he escaped earlier, he could be the one to rescue Harry and keep him away from the Dursleys.
One interesting plot twist could be that the kidnappers turn out to be working for an old enemy of Zuko's family. They initially thought it was just a random act of villainy, but as the story unfolds, they discover a deeper conspiracy aimed at destabilizing the Fire Nation. Another twist might be that Katara discovers she has a hidden power that she can use to help them escape, but using it comes with a great cost. Maybe it drains her life force or has some other negative consequence.
One great 'Zuko and Katara Fanfiction' is 'The Phoenix and the Wave'. It beautifully explores their relationship development. The story is set in a post - war scenario where they have to work together on a diplomatic mission. Their initial distrust slowly turns into mutual respect and something more.