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.
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.
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.
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.
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.
One possible reason could be that Naruto has faced so many betrayals and hardships in the fanfiction. For example, if his friends turned on him for some contrived reasons, it might lead him to stop caring. Another reason could be the constant failure in achieving his goals, like protecting the village but always being undermined by political intrigue within the fan - made story.
One possible reason could be that Naruto's character development leads him to focus more on other aspects like his ninja duties or his bond with other friends. As he grows, his priorities shift.
His character development takes a negative turn. Instead of being the optimistic and determined Naruto we know, he becomes apathetic. His once - strong sense of justice fades away.
He would likely become more responsible. Since he has such a powerful ability, he knows he has to use it for the good of the village. He may start to take on more leadership roles, as he can now analyze situations more thoroughly in the frozen time. He'll also become more empathetic as he can use the time - stopping to understand his friends' and enemies' situations better. For instance, he could stop time to study an enemy's past and find out what made them the way they are, and then try to help them instead of just fighting.