One interesting plot could be Naruto using his future knowledge to prevent some tragic events in the past. For example, he might stop the death of certain characters or change the course of a big battle.
One potential ally could be the younger versions of his existing friends like Sasuke. Even though Sasuke in the past may not be as developed as in Naruto's original timeline, Naruto could still see the potential in him and form an alliance early on.
One big challenge would be not being believed. People in the past might think he's crazy when he talks about future events. Also, he has to be careful not to change too much and disrupt the whole timeline. Another challenge could be that some of the villains in the past might be more powerful than he expected, and he'd have to find a way to defeat them with his current skills and limited knowledge of the past.
Naruto's knowledge from the future could have a huge impact. He might introduce new fighting techniques or ways of thinking that were not present in the past. This could change the balance of power among the ninja villages. Also, his actions could influence the relationships between different clans. For example, if he befriends a clan that was previously isolated, it could lead to new alliances and change the political landscape of the ninja world.
One possible 'sakura sent to past fanfiction' could be about a girl named Sakura who is magically sent back in time to a historical era. She might use her modern knowledge to change things in the past.
Well, Naruto might find allies among the outcasts of the new dimension. People who don't fit in with the mainstream society but have unique powers or skills. They could see Naruto as a kindred spirit and join forces with him. Also, if there are any beings in the new dimension that oppose the forces that brought Naruto there, they could be his allies. They might have their own reasons for wanting to help Naruto, like using his power to overthrow a tyrant in their dimension.
He might be shocked by the advanced technology. There could be new forms of ninjutsu or combat styles. He would also have to adapt to a different social structure.
In a 'Naruto sent to hell' fanfiction, it could be that Naruto is sent to hell as part of a test. The gods or some powerful entities want to see if he can bring hope and change to the damned souls in hell. So, Naruto starts to teach the souls in hell about friendship, perseverance and the ninja way. He tries to reform the place from within, facing many challenges along the way like powerful hell guards and the dark energy that tries to corrupt him.
In some fanfictions where Naruto is sent to hell, he might face various challenges. He could encounter powerful demons who want to harm him. But Naruto, being a strong - willed character, would likely try to fight his way out. He might also meet some other lost souls in hell and try to help them while finding a way back to the living world.