Ainz Ooal Gown is likely one of the most popular. His powerful and mysterious nature makes him a great character to crossover. He can bring his vast knowledge of magic and leadership from Overlord into the RWBY universe. Another popular one might be Albedo. Her loyalty and combat abilities can create interesting dynamics when interacting with RWBY characters. For example, she could form an alliance with a team in RWBY and use her skills to help them in battles.
Ruby Rose is often a popular crossover character. Her positive attitude and powerful scythe - wielding skills can bring a unique dynamic to the Overlord universe. She might befriend some of the more benevolent characters in Overlord or cause chaos with her energetic nature.
One idea could be the characters from RWBY ending up in the world of Overlord. They might initially be confused and have to adapt to the new, more dangerous environment. Maybe Ruby could mistake some of the Overlord's minions for Grimm and attack, causing a stir among the various factions in the Overlord world.
Ruby would be really interesting. Her energetic and optimistic nature would contrast greatly with the often dark and power - hungry characters in the Overlord world. She could inspire some of the downtrodden minions with her belief in the good of people. Also, her scythe skills and speed would be a unique addition to the battles in the Overlord universe.
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.
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.
One idea could be to have Ainz Ooal Gown from Overlord end up in the RWBY world. He could be seen as a powerful new force, and his magic and strategic mind would create a lot of interesting scenarios. Maybe he'd form an alliance with one of the academies, or be seen as a threat by Salem and her forces.
One interesting concept could be the combination of the power systems. In Overlord, there are unique magic and abilities, and in RWBY, there are the Auras and Semblances. Fanfictions might explore how characters from one universe adapt to the power mechanics of the other. For example, how would a character from Overlord use an Aura if they were suddenly in the RWBY world? Another concept could be the cultural clashes. The different races and cultures in Overlord meeting the diverse characters and kingdoms in RWBY could lead to really engaging storylines.
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.