One idea could be that Superman arrives in the RWBY world and has to learn about Dust and its powers. He could team up with Team RWBY to fight a common enemy, like a powerful Grimm that is immune to normal attacks but not to Superman's strength. Another idea is that Ruby discovers she has some Kryptonian-like abilities and Superman helps her understand and control them.
Maybe Salem could be the main antagonist. She has been a long - standing evil force in the RWBY world. If Superman shows up, she would likely view him as an obstacle to her ultimate goal of destroying the world and remaking it in her image. She could use her Grimm army and her own dark magic to fight against Superman and the RWBY characters.
The Mask's influence on the RWBY world might also change the appearance of things. If Weiss were to encounter the Mask, it could transform the elegant and icy settings she's used to into something more zany. The ice sculptures in her family's manor could start dancing around like in a wacky cartoon. And the Grimm, the dark creatures in RWBY, might react in strange ways to the presence of the Mask - perhaps they would be both terrified and strangely attracted to it at the same time.
Maybe there's a rift in the multiverse that pulls He - Man from Eternia and Superman from Earth into a strange new world. They find that their powers are weakened in this new place. So they have to work together, with He - Man teaching Superman about magic and Superman showing He - Man how to better use his strength in a non - magical way, to find a way back to their respective homes.
RWBY crossover RWBY fanfiction can enhance the universe by exploring new relationships. For example, characters who have never interacted much in the original series can form new bonds. This gives a deeper understanding of the characters' personalities. It can also expand on the lore. By mixing different elements from within the RWBY world, new aspects of the history, magic, and technology can be revealed.
Superman could fit into the Marvel Universe in several ways in fanfiction. Firstly, his origin could be tweaked a bit. He could be an experiment gone wrong in a Stark Industries lab that gave him his powers. This would immediately connect him to the Marvel world. His powers would still be his trademark ones like flight, super strength, etc. He could then become a sort of protector of a particular city in the Marvel Universe, like New York. He would interact with the local heroes and villains. His presence would disrupt the power balance a bit, and some villains might target him specifically. But with his unwavering moral compass, he would stand up to them and become an important part of the Marvel Universe's tapestry of heroes.
In a more complex way, their powers could interact on a molecular level. For example, Superman's invulnerability might be enhanced by Invincible's unique cellular structure, or vice versa. They could also share their knowledge of different fighting techniques based on their powers. Since Superman has been a hero for a long time, he could teach Invincible some new ways to use his powers effectively in combat, while Invincible could show Superman some new, more brutal (but effective) ways of taking down opponents.
In a fanfiction, their relationship could also be explored in terms of leadership. Naruto has led his team in many battles and has a sense of responsibility towards his comrades. Raven has her own group and her own way of leading. They could compare and contrast their leadership styles. Maybe they would have some disagreements at first, but as they get to know each other better, they could find a middle ground and lead a combined force against a greater threat in the RWBY universe.
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 common theme is the contrast between their powers and personalities. Superman is all - powerful and has a more optimistic view, while Batman is a normal human with great skills and a darker, more brooding nature. Their interactions based on these differences are often explored.