Naruto might use his Rasengan. It's his signature move and very powerful. He could use it to directly attack the main forces of the invaders, causing chaos among them and disrupting their plans.
Their relationship could develop into a stronger friendship. As they face the challenges of the invasion together, they'll start to trust each other more. For example, Naruto might rely on Temari's knowledge of certain terrains, and Temari would come to respect Naruto's ability to think on his feet in dangerous situations.
The story could change in many ways. For one, Naruto's character development might take a different turn. Instead of being so focused on Sasuke, he could become more involved in the political aspects of the village. His relationships with other characters, like Sakura and Kakashi, might also change. Sakura might be disappointed at first, but then she could see Naruto's new perspective. Kakashi could be proud that Naruto is growing up and making his own decisions.
Sakura might be initially confused. She could be thinking about what she did wrong to make Naruto stop talking to her. Since they have been friends for a long time, this sudden change would be very puzzling for her.
Well, Naruto could stop the invasion in the fanfiction by uniting the village in a way that has never been seen before. He might inspire the shinobi of the village to fight together as one. Maybe he discovers some hidden power within himself, like a connection to an ancient sage, which gives him the strength and knowledge to outwit and overpower the invaders. This power could also allow him to set up powerful barriers or traps to halt the invasion.
One idea could be Naruto being transported to the Young Justice universe during the Invasion arc. He could use his unique jutsu skills like the Rasengan to fight off the invaders. Maybe he teams up with the Young Justice team and teaches them some of his ninja techniques.
One possible reason could be that the fanfiction author wants to focus on other characters. Maybe they feel they've explored Naruto's character enough and want to give more spotlight to characters like Sasuke or Sakura. Another reason might be that the plot of the fanfiction takes a turn where Naruto's acting skills are no longer relevant or needed.
The plot could become more straightforward. Without Naruto's acting, there would be less deception and more direct confrontation. For example, if Naruto was previously acting as a double agent, his true identity being revealed earlier would lead to immediate battles or negotiations.
In a Naruto alien invasion fanfiction, the plot could involve aliens arriving in the Naruto world seeking a powerful chakra source. They might start by attacking small villages to test the strength of the ninja. Naruto and his friends would then have to unite the ninja world, learn about the aliens' technology and weaknesses, and develop new jutsus to fight back. Maybe some aliens could have the ability to absorb chakra, which would pose a great threat.
The plot might involve Naruto and Temari being sent on an invasion mission to stop a new, powerful threat. This threat could be a dark organization that is gathering powerful artifacts. They invade their base to retrieve the artifacts and prevent the organization from using them for evil. Along the way, they might face many powerful foes and have to rely on each other's strengths.