The biggest difference is the creativity of the fanfiction writers. In the anime, the fight follows a set storyline. But in fanfiction, anything can happen. For example, Naruto could suddenly gain a new power that was never in the anime. It's like a whole new world of possibilities.
Konan could be really interesting. In some fanfictions, she might have a different backstory or motivation that affects the Naruto vs Pain fight. For example, she could be secretly trying to stop Pain from going too far in his destruction of the Leaf Village.
Well, Naruto has a great advantage here. When it comes to Kyuubi Naruto, he has access to an incredible amount of chakra. This allows him to perform powerful jutsus and endure long battles. Kiba, on the other hand, depends on his Inuzuka clan techniques which are more physical and based on his partnership with Akamaru. Against the might of the Kyuubi, Kiba would find it extremely difficult to land a decisive blow. So, it's most probable that Naruto would emerge victorious.
One exciting moment could be when Naruto first unleashes a small amount of Kyuubi's chakra, and the shockwave makes Kiba and Akamaru realize the power they're up against. Another moment might be when Kiba tries to use his speed and agility to get close to Naruto, but Naruto quickly counters with a Kyuubi - enhanced Rasengan. And finally, a great moment could be when Naruto goes into a partial Kyuubi transformation, his eyes glowing red, and Kiba has to come up with a last - ditch strategy to try and survive.
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.
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.
Maybe in the fanfiction, Naruto loses his chakra early on in the fight against Pain. But then he discovers a hidden power within himself that is not related to chakra, like a spiritual power from his Uzumaki heritage, which he uses to turn the tables on Pain.
There are many out there. A really good one might focus on the emotional reactions of Team Minato. For example, Minato might be proud of Naruto's strength and how he overcomes Pain. Kakashi could be in awe at Naruto's new techniques. Their reactions can enhance the overall viewing experience in the fanfiction.
The Konoha 12 would likely be in shock. They've seen Naruto grow, but this fight against Pain is on a whole new level. Some, like Shikamaru, would immediately start analyzing the battle strategies. Sakura might be worried sick about Naruto's safety, while Kiba could be cheering Naruto on loudly, impressed by his power.