Naruto is an obvious choice as they have an existing relationship in the original series. Their interactions can be further explored and developed in fanfiction.
Naruto is often paired with Ebisu Sensei in fanfiction. Since Ebisu was assigned to train Naruto at one point, many fanfictions build on that relationship, showing how Naruto grows under his tutelage and how Ebisu has to adapt to Naruto's unorthodox ways.
The 'jiraiya vs pain' in RWBY fanfiction could be a battle of wits as much as a battle of powers. Jiraiya is a very experienced ninja, and Pain has his own ideology - driven powers. In a RWBY setting, the battle could be affected by things like Dust, the special energy source in RWBY. Jiraiya might be confused by this new element at first, while Pain could try to incorporate it into his attacks. It would be a clash of two different power systems and fighting styles.
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.
Naruto Ebisu fanfics are special because Ebisu is a rather underrated character in the original series. Fanfics give him a chance to shine. For example, they can explore his relationship with Naruto in more depth. Maybe Ebisu has some hidden skills or knowledge that he imparts to Naruto in these stories.
One great Naruto Ebisu fanfic is 'Ebisu's Hidden Potential'. It delves into Ebisu's backstory more deeply. It shows how he trained in his early days and his relationships with other characters like Iruka. Another interesting one is 'Ebisu in the Shadows'. This fanfic focuses on Ebisu's role in some of the village's secret missions that are not shown in the original series.
It's really hard to say who would win. Jiraiya has his Sage Mode which gives him enhanced strength, speed, and perception. But Pain has the Rinnegan which allows him to use powerful abilities like the Six Paths techniques. In the RWBY fanfiction context, it might depend on how well they adapt to the RWBY world. If Jiraiya can quickly figure out how to use Dust to his advantage, he might have an edge. But if Pain can use his powers to disrupt the balance of the RWBY world, he could also come out on top.
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.