It could be some sort of new villain created specifically for this fanfiction. Maybe a dark ninja - bender hybrid who wants to take over both the Naruto and Aang's worlds. Naruto and Aang would have to team up to defeat this new and powerful enemy.
One could be Ozai from Aang's world. He might be even more powerful in this fanfiction and Naruto has to step in to help Aang deal with him. Naruto's unique skills and abilities would be crucial in countering Ozai's firebending.
Well, one possible plot could be that Naruto uses his shadow clone jutsu to create multiple clones to help Aang with his airbending training. Naruto's clones can act as moving targets or opponents for Aang to practice his dodging and offensive airbending skills on.
Naruto's experience in handling loss and grief can be of great value to Aang. Both have lost important people in their lives. Naruto can show Aang how to turn that pain into strength. By sharing his own journey of dealing with the death of his loved ones and still moving forward, Naruto can help Aang not be consumed by his own losses and instead use them to fuel his growth as the Avatar.
Well, one possibility could be that Naruto, with his years of experience, teaches Aang some advanced combat techniques. Maybe Naruto shows Aang how to better use the airbending in a more strategic way during battles. For example, Naruto might teach Aang how to combine airbending with quick movements like his own shadow clone jutsu - using clones to create distractions while Aang attacks from unexpected angles with his airbending.
It could be a variety of villains. Maybe some of the traditional Naruto villains like Orochimaru or Pain could be in the story and Naruto kills them. Or perhaps in this fanfiction crossover, there are new villains created that are a combination of Naruto - style threats and Justice League - type menaces. It's hard to say exactly without reading the fanfiction, but it would be interesting if it included some well - known Naruto baddies being taken out by Naruto in a new setting with the Justice League around.
Obviously, Naruto is one of the main characters as the title indicates he is the one helping. Mikoto and Hitomi are also main characters. Mikoto might be a character with her own set of skills and a backstory that makes her need Naruto's help. Hitomi could be in a similar situation, perhaps a bit more vulnerable or in a difficult position that only Naruto can assist her out of.
It could be the classic villains from the original series like All For One. He might be interested in baby Deku's potential quirk. Another could be Shigaraki, who might see baby Deku as either a threat or an opportunity to disrupt the hero world in a new way.
Another one is Goro. He's a petty thief in Naruto fanfiction who has a special skill of being able to blend into the shadows. He steals from local merchants in Konoha. Goro may not seem like a big threat at first, but his actions can sometimes lead to bigger problems, like when he steals important items that are needed for a mission.
The Akatsuki could still be the main villains. In a secret agent Naruto fanfic, they could be even more devious, using undercover agents of their own to disrupt the shinobi world while Naruto tries to stop their grand plan of collecting all the tailed beasts.
The demons from Inuyasha's world that resent the idea of a half - human, half - demon having such a powerful combination of abilities could be villains. They might see Naruto as a threat to their existence or way of life and try to eliminate him. Also, there could be ninja who are jealous of Naruto's newfound powers and team up with these demons to take him down.
In the 'Naruto Saves Luffy and Ace Fanfiction', the main villains might include the World Government from One Piece. They have a lot of power and resources and are often against pirates. Also, there could be some rogue ninjas from Naruto's universe who are attracted by the chaos and want to take advantage of the situation. These villains would pose a great threat to Naruto's mission of saving Luffy and Ace, making the story full of tension and conflict.