Maybe there are some power - hungry individuals within other tribes who envy the airbenders' abilities and want to either control or destroy them. So they become the antagonists in the fanfiction.
It could be the Fire Nation remnants who still hold grudges against the airbenders. They might be trying to finish what they started years ago.
There could be a group of dark benders who want to steal the airbending powers for their own evil purposes. They see the airbenders as easy targets to fulfill their dark desires.
One interesting plot point could be how Aang uses his unique airbending skills in new and creative ways to protect the airbenders. Maybe he discovers ancient airbending techniques that are long forgotten and uses them to fend off enemies. Another could be the relationships he forms with other airbenders during the protection process, which might include some internal conflicts within the airbender community.
In 'aang honors the airbenders fanfiction', the theme of remembrance and respect stands out. Aang would surely focus on remembering the great airbenders of the past. He might do this by performing ancient airbending rituals, passing on the stories of his predecessors to the new generations. Additionally, the theme of hope could be there. By honoring the airbenders, he gives hope to the future that their legacy will not be forgotten and will continue to influence the world of bending.
Aang is obviously the most important character as the title implies that he is the one honoring the Airbenders. His friends like Katara, Sokka, and Toph might also be important. Katara could be there to support Aang in his journey of honoring his people. Sokka might offer his strategic thinking and humor. Toph, with her earthbending skills, could also play a role, perhaps in protecting Aang during his efforts to honor the Airbenders.
Aang could save the Airbenders in the fanfiction by first finding out the root of the threat they are facing. If it's a powerful enemy bent on destroying them, he may seek allies among the other benders, like the Earth Kingdom or the Water Tribes. He'd then use his airbending to scout the enemy's territory undetected. Once he has all the information, he could use his skills to either directly confront the enemy or find a way to neutralize the threat. For instance, if the enemy is using some sort of dark magic, Aang could use his pure Avatar energy to dispel it and free the captured Airbenders. And of course, he'd use his airbending to fly around and quickly transport the Airbenders to a secure location.
Maybe there are powerful dark sorcerers. These sorcerers could be trying to capture Naruto for their own evil purposes, like using his power to open a portal to a dark dimension or something, and Kurama has to protect him from them.
Maybe some of Tony's business rivals who have access to advanced technology. They could be jealous of Tony's relationship with Ultron and try to harm him. They might hire mercenaries or develop their own weapons to go after Tony. In this fanfiction, these rivals would be the main antagonists as they constantly try to break through Ultron's protection of Tony.
In many cases, the main antagonists can be other Slytherins who still hold grudges against Harry or are loyal to the pure - blood supremacist ideology. They might see Harry as a threat to their way of life. Also, some Death Eaters can be antagonists. They target Harry because of his role in Voldemort's downfall and would stop at nothing to get to him.
Perhaps there are some shinobi within the village who are jealous of Naruto's potential. They might try to harm Naruto in secret, and Hiruzen has to be vigilant against them. These shinobi could be from clans that have rivalries with the Uzumaki or those who just don't want a new powerful force emerging in the village.
Some fanfictions might introduce new original antagonists. These could be powerful rogue ninjas who are after Sakura for her medical skills or some special power she might have in that particular fanfiction. They would then be the main threats that Itachi has to deal with to protect her.
One challenge could be the strength of the enemy. If the enemy is very powerful, it would be difficult for Aang to overcome them alone. Another challenge might be the lack of resources. He may need certain items or help from others to save the Airbenders but not be able to get them easily.