The RWBY characters would need to rely on their combat skills in this new world. However, they'd also have to learn to communicate with the apes. They could start by observing the apes' behavior and gestures. Ruby's leadership skills might come in handy as she tries to form alliances with different ape groups. Weiss could use her knowledge of strategy to help them survive in the ape - dominated environment. Blake and Yang would contribute with their physical strength and combat experience, all while trying to adapt to the new social norms.
Adapting to the ape - dominated world would be a huge challenge for the RWBY characters. They'd first have to get over the shock of seeing a world where apes are in charge. Ruby, being the optimistic and adventurous one, would likely lead the way in exploring and understanding this new world. Weiss would need to set aside her pride and learn from the apes. Blake, with her empathetic nature, could build relationships with the apes. Yang, on the other hand, would have to control her temper as the apes' ways might be different from what she's used to. They'd all have to find ways to use their Semblances and weapons effectively in this new and strange environment, while also respecting the apes' territory and social hierarchies.
Ruby would probably be very curious at first. Her adaptable nature would help her start learning about the apes' ways quickly. Weiss might have some trouble due to her more refined upbringing, but she could use her intelligence to find common ground. Blake, with her experience of being an outcast, could potentially understand the apes' struggle for their own place in the world better. Yang would likely be ready to fight if the situation called for it, but also try to find peaceful solutions.
Madara would have to adapt to the different threats in RWBY, mainly the Grimm. In his world, he was used to fighting other shinobi and clans. The Grimm are a whole new type of enemy. However, his Sharingan would give him an advantage in detecting their movements. He might also try to find a way to use the Grimm's negative energy, similar to how he used negative emotions in his own world to fuel his power.
One interesting crossover could be the characters from RWBY finding themselves in the world of Planet of the Apes. They might have to deal with the complex social structures of the apes while also using their own unique abilities. For example, Ruby's speed could be a great asset in escaping from some of the more dangerous ape tribes. Another aspect could be the apes being intrigued by the technology and magic that the RWBY characters possess.
Ruby would adapt quickly as she's always eager for new challenges. She'd see Spider - Man's powers as a cool new set of skills to master. Weiss would initially struggle with the more unorthodox and street - level nature of Spider - Man's world but would eventually use her intelligence to her advantage. Blake would be good at adapting due to her own experience of living on the fringes. Yang would be all about the action and would jump right into using Spider - Man - like powers without hesitation.
Ruby would probably be excited by the new and different kinds of challenges in the Fallout world. She'd quickly learn to use the weapons she finds there while still relying on her Crescent Rose. Weiss would have a harder time adapting to the dirt and grime, but her determination would make her find ways to use her magic in this new environment. Blake would likely be more at ease in the shadows of the ruined buildings, using her stealth to her advantage.
In a fanfiction, RWBY's adaptation to Earth life would be a complex process. Ruby would be drawn to the bright and shiny aspects of Earth, like big cities and new gadgets. She might start a blog or a YouTube channel about her experiences. Weiss would struggle at first with the lack of the familiar caste system from Remnant. But she'd eventually find her place, perhaps in the art or fashion world on Earth. Blake would be on the lookout for any signs of discrimination similar to what the Faunus face on Remnant. She might get involved in activism if she found such issues. Yang would be all about experiencing new thrills. She could become a popular figure in extreme sports or in local bars where she'd show off her strength in friendly competitions. Their Semblances would also play a role. Ruby's speed could make her a star athlete, Weiss' glyphs could be used in magic shows (if Earth has something like that), Blake's shadow - like abilities could be used for cool stunts, and Yang's strength would always be an attention - getter.
RWBY characters would likely adapt in different ways. Weiss, being from a more refined background, might study the Pokemon world meticulously. She could read up on Pokemon types and their strengths and weaknesses, and then apply her knowledge to build a strong team. Blake, with her stealthy nature, could use her skills to observe Pokemon in the wild and learn their behaviors, which would help her in training and battles. Yang, with her strength, could bond with physically powerful Pokemon and learn to control their power in battles through her own experience of handling her own strength.
Ruby would need to adapt to the food in the real world. In Remnant, they might have different kinds of food based on their regions and cultures. Here, she'd be introduced to a whole variety of new tastes. She might find some things delicious, like pizza perhaps, but also be really confused by things like fast food chains. Also, she'd have to get used to the currency system. Without any money at first, she'd have to figure out how to earn or get some in order to survive.
Ruby's speed and scythe - fighting skills could be seen as a unique form of combat in the Naruto world. Her speed might be compared to that of some of the faster ninja like Rock Lee. Her scythe could be modified with chakra - based enhancements. Weiss's Glyphs could be related to some form of ninjutsu seals. She could use her Dust - infused attacks in combination with ninja techniques. Blake's shadow clones and her acrobatic combat style could be similar to some ninja's stealth and agility - based fighting. Yang's strength could be on par with some of the physically strong ninja like Tsunade, and her ability to absorb and release energy could be a new concept in the Naruto world.
The OC might interact with them in various ways. They could start by being in awe of their combat skills, like Ruby's speed. And in the harem aspect, they could show affection differently to each character. For Weiss, it could be through respecting her family name and helping her with her studies. With Blake, they might bond over books and their love for knowledge.
Well, they'd first have to deal with Salem's powers. It's not easy to suddenly have such great and dark powers. They might struggle to control them at first. For example, Salem can manipulate Grimm, and the reincarnated 'Si' might accidentally summon Grimm when they don't mean to, causing chaos in the areas around them.