One idea could be exploring a different backstory for Pain. Maybe he had a secret friendship with a Konoha ninja before turning to his dark path. This could add a new layer of complexity to his character and the conflict in the arc.
A healer from a far - off land who has a special ability to not only heal physical wounds but also emotional traumas. This character could be drawn to Konoha during the Pain Arc because they sense the great pain and suffering. They could interact with Naruto and help him deal with his own inner turmoil in a different way, while also having their own sub - plot of trying to understand the nature of the ninja world.
One possible cause could be his sense of failure. Naruto always wants to protect his friends and village, so if he fails in a mission or is unable to save someone, it can cause him great pain.
One interesting Naruto arc fanfiction could be about an alternate ending to the Pain arc. Maybe Naruto finds a different way to convince Pain without using brute force. Another could be a fanfiction set during the Chunin Exams arc, where a minor character gets more spotlight and changes the course of the exams in a unique way. There are also fanfictions that explore what would happen if Naruto was raised by different people during his early life in the Hidden Leaf Village arc.
The first story arc of Naruto concludes approximately at episode 21. It's marked by the resolution of certain key events and the advancement of the overall plot. However, the exact determination can be subjective based on individual interpretations.
Well, 'Naruto meets Pain: The Alternate Ending' is a cool fanfic. In this story, Naruto uses a completely different strategy when facing Pain that we don't see in the original anime. It makes for a very exciting read. There's also 'Naruto and Pain: A Reconciliation' which explores what would happen if Naruto managed to convince Pain to change his ways much earlier in their encounter.
There's also 'The Bond of Enemies'. In this fanfic, Pain, after his defeat, is given a second chance at life by Naruto. It shows a really interesting dynamic as Pain tries to figure out his new place in the world with Naruto's influence. It has some great action scenes and emotional moments.
It could be about Naruto having some sort of connection to Pain. Maybe in this fanfiction, Naruto is somehow related to Pain in a way that wasn't in the original story, like being his son in an alternate universe. This could lead to a whole new set of storylines, with Naruto perhaps having to deal with the legacy of Pain while also following his own path as a ninja.
In some fanfictions, Naruto might become more strategic during the Wave arc. He could learn from his mistakes faster and start to think several steps ahead in battles, instead of just charging in blindly like he sometimes does in the original story.