Definitely Ruby Rose. Since she's the main protagonist in RWBY, it's likely that Natsu would cross paths with her first. Their personalities are quite different, with Ruby being more innocent and Natsu being more brash, so their interactions would be interesting.
Well, it could be about Natsu finding himself in the RWBY universe and having to adapt to the different combat styles there. Maybe he teams up with the RWBY characters to fight a common enemy.
Well, Romeo is often depicted as a passionate character. In the context of a fanfic, he might show intense emotions towards Natsu. Natsu, on the other hand, could be shown as strong - willed yet having a soft side when it comes to Romeo. But it really depends on how the author interprets them in the fanfic.
I highly doubt it's a popular fanfic given the rather inappropriate and unclear title. Most popular fanfics usually have more engaging and appropriate titles that give a better sense of the story.
One idea could be a fanfic that explores the backstories of minor characters in RWBY more deeply. For example, you could focus on a character like Velvet and create a story about her training before coming to Beacon. Another could be a crossover within the RWBY universe itself, like a team-up between different schools' teams that we haven't seen much of in the official series.
In Natsu x Erza fanfic, their relationship can be full of adventure - based camaraderie. Natsu is often depicted as the impulsive and powerful mage, while Erza is the strong - willed and disciplined one. They might team up frequently, with Natsu's spontaneity contrasting Erza's calculated moves. This can lead to interesting character dynamics, where they both learn from each other and grow together in their fictional adventures.
In addition to Natsu, Wendy could be a main character in the 'natsu is a dragon god fanfic'. Since she also has dragon - related powers, she could have a special connection with Natsu in this new situation. Maybe she helps him understand more about his dragon god powers. And Makarov, as the guild master of Fairy Tail, would also be a significant character. He would be concerned about how Natsu's new status affects the guild and the magical world as a whole.
It's not acceptable. The RWBY franchise promotes values such as equality, self - improvement, and unity. A'slave fanfic' would violate these values. Moreover, it could also create a negative environment within the fandom. Fanfics are supposed to add to the enjoyment and exploration of the RWBY universe in a positive way, and this type of fanfic clearly does not do that. It's better to focus on fanfics that are more in line with the positive and inspiring nature of RWBY.