Kaneki Ken could fit in as an outsider with a dark past, much like some RWBY characters. His struggle with his dual nature as a human - ghoul could parallel the internal conflicts of RWBY characters dealing with their own powers and identities. For example, Ruby's journey to understand her silver - eyed warrior powers.
Kaneki's relationships in the RWBY universe in fanfiction could be complex. He might form a bond with Blake, as she also has a connection to a group that is feared (the Faunus). Or he could have a rivalry with Yang, as their personalities are quite different. His presence would surely stir up the dynamics among the RWBY characters.
Grimlock's abilities are very physical and brute - force based. In the RWBY universe where there are a variety of Semblances and Dust - based powers, his raw power would stand out. His durability would allow him to withstand attacks from powerful Grimm. And his combat skills, which are more instinctual, could be an interesting contrast to the more refined fighting styles of the RWBY characters. He could also potentially use some RWBY - specific elements like Dust to enhance his already powerful attacks.
In a 'noctis in rwby fanfiction', Noctis' ability to use magic, like his elemental attacks, would be a significant factor. In the RWBY world, magic is a somewhat mysterious and not - fully - explored aspect. Noctis could introduce new forms of elemental combat. His fire - based attacks could be used to counter ice - type Grimm, and his lightning attacks could stun enemies, allowing his RWBY allies to deliver finishing blows. Also, his ability to enhance his physical abilities with magic, such as increased strength or speed, would make him a formidable ally in battles against the powerful Grimm and any human adversaries that might arise.
In a Pirates of the Caribbean fanfiction, Ruby could be seen as a sort of chosen one. Her innocence and determination could be what's needed to break a powerful curse. Weiss might form an unlikely alliance with a crusty old pirate who teaches her the ropes of the sea. Blake could discover a hidden community of Faunus - like beings in the Pirate world, and Yang would befriend some of the rowdiest pirates and show them that there's more to strength than just brute force.
A half - Grimm OC could fit in as an outcast. Since Grimm are the enemies in the RWBY universe, a half - Grimm would be seen with suspicion. But they could also be a key to understanding the Grimm better. For instance, they might be able to detect hidden Grimm lairs or weaknesses that others can't. They could team up with the main characters like Ruby and the others, gradually earning their trust through their unique skills.
One interesting story could be about Kaneki Ken's unique abilities being introduced into the RWBY world and how he teams up with Team RWBY. Maybe his kagune could be a new form of combat power that the RWBY characters have never seen before.
Blake could be a bit of an enigma in Middle - earth. She might have some similarities to the Rangers, as she is used to being on her own and is very stealthy. Her faunus heritage could also add an interesting dynamic, as she could have some unique abilities that are different from the normal races in Middle - earth. Yang, with her strength and courage, would be a great addition to any battle. She could be like a female version of Gimli, always ready for a fight and not afraid to take on powerful enemies.
Harry Potter himself could be seen as a kind of foreign wizard in the RWBY world. He might be initially confused by the concept of Dust but quickly adapt and use his magic to enhance the RWBY team's capabilities. Hermione would probably be fascinated by the study of Dust and Semblances, and use her vast knowledge to help bridge the gap between the two magic systems. Ron could be the one who forms quick friendships with the RWBY characters, sharing his sense of humor and loyalty.
He could be integrated as a powerful enemy at first. He might target the academies because he sees them as places that are trying to control and limit power, which goes against his own philosophy. However, as the story progresses, he could have a change of heart after seeing the selfless acts of the RWBY characters. He could then use his powers to help them against a common enemy like Salem.
Sephiroth would be a very powerful and somewhat out - of - place character. His long silver hair and his calm, menacing demeanor would make him stand out. He'd likely be seen as a mysterious figure. His combat abilities would make him a valuable asset in the fight against Titans, but his motives might be questioned as he's not from that world.
Well, Bruce Wayne could bring his detective skills. He's like a super detective in his own world. In RWBY, he could help uncover secrets about the Grimm or the various factions. Maybe he'd team up with Team RWBY and use his martial arts skills in combat against the bad guys.