Well, they might be really shocked at the power levels of Goku and Broly. RWBY characters are used to their own kind of battles, and seeing the insane energy blasts and transformations in the Goku vs Broly fanfic could leave them in awe. They might start thinking about how they could incorporate some of those powerful moves into their own fighting styles.
In a Goku vs Broly crossover fanfiction, anime characters could have different reactions. Some might see Goku as a symbol of justice and be inspired by his never - give - up attitude. On the other hand, Broly's raw power could intimidate those who value brute strength. And there could also be characters who try to interfere in the fight for their own motives, like to stop the destruction that such a powerful battle could cause.
Goku could escape by overpowering Broly. He might tap into his Super Saiyan forms, like going into Super Saiyan Blue or even Ultra Instinct if he's pushed far enough. His sheer power and fighting skills could allow him to break free from whatever restraints Broly has put on him.
If anime characters are in awe, they might stay out of the fight and just be observers, which could keep the focus mainly on Goku and Broly. So the plot would be a more straightforward battle between the two.
One possible storyline could be that Naruto is somehow transported to Goku Black's universe. There, he has to face Goku Black who sees him as an intruder. Naruto would have to quickly learn about Goku Black's powers and find a way to fight back using his ninja skills. Another storyline could be that a powerful villain creates a rift between their two universes and pits them against each other. They start off as enemies but then realize they are being manipulated and team up to fight the real villain.
There could be a storyline where Beerus, out of boredom, decides to train Goku Black instead of fighting him. But Goku Black misinterprets this as a sign of weakness and attacks Beerus. This could lead to a battle where Beerus has to hold back at first to avoid killing Goku Black, but as the fight progresses, he realizes he has to use his full power to subdue him.
Sure. Fanfiction writers have a lot of creative freedom when it comes to Goku and Female Broly. In some fanfictions, they might be in a romantic relationship, which is an interesting take considering their Saiyan heritage and the way they both value strength. However, not all fanfictions take this route. Some might explore a more platonic friendship where they respect each other's power and learn from one another. You can usually find a variety of these stories by using the search function on major fanfiction platforms.
One possible storyline could be that Goku Black arrives on Earth in search of a powerful energy source. The Justice League detects his arrival and confronts him. At first, they underestimate his power. Goku Black easily defeats some of the members, but then the League starts to work together and figure out his weaknesses. Another storyline could be that an evil entity has brought Goku Black to the DC Universe to cause chaos and the Justice League has to stop him while also dealing with the entity. Or perhaps Goku Black is tricked into thinking the Justice League are enemies of the Saiyans and he attacks them, only to later find out the truth and have to team up with them to fight a greater threat.
The different interpretations of the characters are great. In some fanfictions, Goku Black might be portrayed as even more evil or cunning than in the original series, and Hit could be shown with new strategies. For instance, a fanfiction might have Hit teaming up with other characters from different universes to take on Goku Black, which adds a whole new dimension to the story.