One idea could be a crossover where Goku somehow ends up in the RWBY universe. He could train the RWBY characters, sharing his martial arts knowledge and helping them improve their combat skills. For example, he could teach Ruby how to better control her speed and use her scythe more effectively in combat.
A story where Goku teams up with Team RWBY to fight a common enemy could also be great. Maybe an ancient and powerful being from Goku's universe that has somehow found its way into the RWBY world. They would have to combine their different fighting styles and powers to defeat this foe.
One idea could be that Goku accidentally travels to the RWBY universe during a sparring session that goes wrong with Whis. He could be mistaken for a powerful Grimm at first, causing chaos. Then, he teams up with Team RWBY to fight a new super - strong Grimm that threatens all of Remnant.
The transformation aspect could also be explored. Goku Black has his different forms in the Dragon Ball series. In RWBY fanfiction, these forms could be affected by the Aura or magic in the RWBY world. Maybe his Super Saiyan forms could be enhanced or restricted by the unique rules of RWBY.
A Goku crossover with the Pokémon world could be really fun. Goku could try to catch Pokémon using his speed and strength. He might also team up with Ash to battle powerful Pokémon trainers. Or how about a crossover with the Digimon world? Goku could enter the Digital World and help the Digimon in their battles against evil Digimon using his energy attacks.
One idea could be a story where Goku and Kefla have to team up to face a new, powerful enemy that neither could defeat alone. They start off not trusting each other much, but as they fight side by side, they learn to respect one another's strength and fighting styles.
One interesting idea could be a crossover of different timelines within RWBY. For example, characters from the past meet the current ones and have to deal with the differences in their worlds. Another could be a crossover of different teams in unexpected ways, like Team RWBY having to team up with a rival team to face a common enemy that is more powerful than any they've faced before. And sometimes, there are crossovers that involve alternate versions of the characters, where their personalities or abilities are slightly different, which can lead to very unique and engaging storylines.
One idea could be that Goku and Goku Black are forced to team up against an even greater threat from another universe. They start to understand each other's fighting styles during the battle and gradually develop a grudging respect for one another.
In some versions, the female Goku could be part of a prophecy. The two Gokus meet, and at first, there is some confusion and misunderstanding. But as they get to know each other, they discover that they are key to fulfilling the prophecy. They combine their powers and defeat an ancient evil that was threatening both of their worlds.
There are multiple factors. Firstly, the fanfiction allows for exploration of new storylines that the original shows might not cover. For instance, a fanfiction could explore what would happen if Goku Black was brought to the RWBY world and had to team up with the main characters to fight a common enemy. Secondly, the fanfiction can play with the different aesthetics of the two universes. The bright and colorful world of RWBY contrasted with the more intense and action - packed world of Goku Black can create a visually and thematically interesting blend. Moreover, the fanfiction gives fans the freedom to reshape and reimagine the characters in new and exciting ways.
One idea could be Goku becoming more cynical. Maybe after facing a great loss, he loses his usual optimistic view of battles and training. Instead of seeing every fight as a chance to grow, he starts to question the point of it all.
One idea could be a story where Bulma creates a new device that accidentally sends Goku and her to a parallel universe. There, they have to work together to find a way back home while facing new and strange enemies. Another could be a time - travel plot where they go back in time to before Goku met Chi - Chi and Bulma realizes she has feelings for him. The third idea is a story where Goku and Bulma get trapped on a deserted planet and must rely on each other's skills to survive and escape.