Well, the Naruto vs Pain fight in the original series is epic. Fanfiction allows fans to explore different scenarios and what - ifs. Maybe they want to see different character developments during that intense battle.
The plot should be engaging. It could add new twists to the Naruto vs Pain battle. Maybe introduce some new jutsus or strategies that make the fight even more exciting. Also, good fanfictions in this category usually have a good balance between action and the emotional aspects of the characters.
The outcome in this fanfiction could be a draw. Naruto and Hinata would put up a great fight against Pain. Naruto would be all fired up, using his Rasengan and other ninjutsu. Hinata would be there, protecting Naruto's blind spots with her gentle fist techniques. But Pain is no pushover. His ability to control gravity and rain down destruction could keep Naruto and Hinata at bay, leading to a situation where neither side can fully defeat the other.
One of the most popular is 'Naruto Shippuden: Sakura Hiden - Thoughts of Love, Riding Upon a Spring Breeze'. It's popular because it shows Sakura in a new light, with her own adventures and growth.
In the original Naruto vs Pain fight, there were many unanswered questions. Fanfiction tries to answer those. For example, what if Naruto had more help? Or what if Pain had different motives? This makes it appealing to fans who want to explore these ideas.
I don't think it's strange at all. Naruto is a very curious person. Fanfiction can offer new perspectives on his own life and the lives of his friends. He might learn something new about himself or get inspired by the creative ideas in the fanfiction. It could also be a form of entertainment for him during his downtime.
A Naruto x Hinata fanfiction could focus on a mission they go on together during Naruto Shippuden. They are forced to rely on each other in a dangerous situation. Hinata gets injured protecting Naruto, and Naruto is filled with a new - found determination to protect her. This experience deepens their bond, and Naruto starts to see Hinata in a whole new light, leading to the start of their romantic relationship.