One common theme is redemption. Pain is often depicted as a character who can be redeemed through his interactions with Hinata. For example, Hinata's unwavering belief in the good of people might make Pain question his own actions.
One possible plot is that Pain targets Hinata to get to Naruto. Since Hinata has a special place in Naruto's heart, Pain might think that by hurting her, he can break Naruto. But Hinata shows great courage and Naruto comes to her rescue.
Hinata saving Naruto from Pain in fanfiction can take on many forms. It could be that Hinata has been secretly training and has a new set of abilities that she unleashes to save Naruto. This not only changes the course of the battle but also the dynamics between the characters. Fanfic writers might also add some emotional elements, such as Hinata's inner thoughts and feelings during the rescue. This makes the story more engaging and gives readers a fresh perspective on the Naruto - Hinata relationship.
It's hard to say for sure. If the fanfiction focuses on Hinata's growth, she could potentially defeat Pain through her own skills and some unexpected twists. But Naruto is also likely to be a major factor, so it could be a combined effort of both of them that overcomes Pain.
In this fanfiction, Naruto might be extremely enraged seeing Hinata in danger against Pain. Hinata, on the other hand, would likely show her newfound strength and determination. Maybe she'd manage to land a few surprise attacks on Pain before Naruto fully jumps into the fray.
In such a fanfic, it might explore the emotional turmoil. Pain's attacks on the village would not only be a physical threat but also an emotional one. Hinata could be in a position where she has to choose between her love for Naruto and her duty to the village. Naruto, on the other hand, would be dealing with his own feelings for Hinata while trying to defeat Pain. And Pain himself could be presented with more complex motives, perhaps having some sort of connection to Naruto's past that is revealed during the battle.
You can try searching on some popular fanfiction websites like FanFiction.net or Archive of Our Own. They usually have a large collection of fanfictions including ones about hinata and pain.
Maybe Orochimaru's former followers who are still lurking in the shadows. They see Naruto as a threat and Hinata as an easy target to get to Naruto. Another possibility could be some power - hungry shinobi from other villages who view Konoha as weak after the Pain incident. They might target Naruto and Hinata as key figures in Konoha's future to try and undermine the village's rebuilding efforts.
One possible plot could be that Hinata and Naruto start to train together more intensively. After facing Pain, Naruto realizes Hinata's feelings for him more deeply. They could go on missions side by side, and Hinata becomes stronger under Naruto's influence. Naruto, in turn, starts to see Hinata as not just a friend but someone he could potentially have a future with.