Another possibility is that the main antagonist could be a new, mysterious force. Maybe it's a group that has been secretly manipulating events from the shadows. They see Naruto as a key figure to either eliminate or control. They could have some sort of ulterior motive related to the ninja world's power balance or some ancient prophecy that Naruto's presence disrupts.
It could be a rogue ninja from another village who sees Naruto's victory as a threat to their own plans. Maybe they were planning some sort of takeover or power play and Naruto's new - found status throws a wrench in their plans.
Well, one possible plot could be Naruto coming back to the village and being hailed as a hero. He might then focus on rebuilding the parts of the village that were damaged during the Pain attack. He could also start training the next generation of ninja, sharing his newfound wisdom and strength.
In this kind of fanfiction, Naruto might be welcomed as a hero. The village could start to rebuild with his leadership. People would look at him with newfound respect and admiration.
It could be a rogue ninja from a neighboring village who has a vendetta against Konoha. This ninja might see Naruto's return as an opportunity to take on the strongest ninja in Konoha and prove his own strength.
He could meet Hinata, and their relationship might develop further. Maybe she would be the first to greet him and express her admiration more openly.
A new character could be the main antagonist. This character could be from a far - off land that Naruto has never encountered before. This antagonist has heard of Naruto's power and wants to prove himself by defeating Naruto and taking over the Hidden Leaf. He might have unique powers and a large army at his disposal. He could also be manipulating some of the villagers from the inside to create chaos before making his big move.
Often, Naruto's relationships with other characters are explored further. He might have deeper conversations with Sasuke, trying to convince him to come back to the village for good. His bond with Sakura could also develop in different ways, perhaps becoming a stronger friendship or even something more romantic in some fanfictions.
It could be a new villain who has risen to power during Naruto's absence. This villain might have a vendetta against Konoha or the ninja world in general because of something that happened while Naruto was away.
Perhaps it's an old enemy who has somehow managed to come back stronger. Maybe someone from Orochimaru's old experiments that went wrong, but instead of dying, they gained some dark and powerful abilities. They see Naruto's return as a threat to their plans of world domination, so they target Konoha first. They might be able to control dark chakra in a way that no one has seen before, and use it to create chaos and destruction. They could also have some minions who are equally as powerful and loyal to them, making them a formidable foe for Naruto and Konoha.
It could be an unknown ninja who has been researching dark and forbidden arts. This ninja accidentally unleashes the Black Death - like plague while trying to gain ultimate power.
Perhaps an old enemy that Naruto thought was defeated has returned, stronger than ever. This enemy could hold a grudge against Naruto and the elemental nations for past defeats and wants revenge.