An overpowered OC can fit in by having a specific role or purpose that doesn't overshadow the main characters all the time. Maybe they are powerful but are only focused on a particular aspect of the RWBY world, like protecting a certain area from Grimm. Their power is then contained within that scope, not disrupting the overall balance of the story.
A Dragonborn OC can fit into the RWBY universe by having their own unique backstory related to dragons. For example, they could have been born in a world where dragons were both feared and revered. When they enter the RWBY universe, their dragon - like abilities such as enhanced speed, strength, and the ability to breathe fire or ice can make them stand out. They could become a new type of huntsman or huntress, using their powers for good.
Well, one way is if the OC's overpowered abilities are tied to an ancient artifact or power source that is suddenly unearthed in the Naruto world. This would draw the attention of all the characters. The OC could start as an outcast because of their strange and powerful abilities but as the story progresses, they find common ground with the likes of Naruto and his friends. For instance, if their power is related to a long - forgotten Sage Mode, they could share their knowledge and help in the fight against common enemies, while also having their own character arc of learning to control and use their power responsibly within the framework of the Naruto universe.
An OC can fit in as a new ally or enemy. For example, if the OC is a vampire hunter, they would be an enemy to the Originals. But if they are a witch offering help against a common threat, they could be an ally.
The gamer with stands could fit into the RWBY fanfiction world by becoming a sort of mentor or a unique ally. Their stands could have powers that are not seen in the RWBY universe before. For example, a stand that can teleport short distances could be used to quickly rescue RWBY characters in danger. The gamer could also introduce new concepts from the gaming world, like unique strategies or power - up systems, which could be adapted by the RWBY characters to become stronger and better at fighting the Grimm.
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.
They can also have a connection to the vampire lore in the Lost Boys universe. Maybe the OC has studied vampires in secret and is eager to prove their theories when they meet the real deal. This way, they can interact with the characters in a more meaningful way and contribute to the story.
They can fit in through relationships. A merman OC could befriend students or teachers at Hogwarts. Maybe a merman forms a bond with Hagrid, who is known for his love of all creatures. This friendship could lead to adventures where the merman's knowledge of the underwater world and Hagrid's knowledge of the Forbidden Forest combine in unexpected ways.
Arthur Morgan could fit in as a mentor figure. His experience in combat and dealing with difficult situations would make him a great teacher for the RWBY students. For example, he could show them how to be more resourceful in the wild, which would be useful when they are on missions in less - civilized areas.
The OC could be an apprentice to one of the magical characters in the Mary Poppins universe. Let's say the OC is apprenticing under Bert. They learn how to do all his odd jobs and also pick up some of his charm and showmanship. When Mary Poppins returns, the OC is in the middle of learning a difficult dance routine from Bert. MaryPoppins then helps the OC master it, and together they use the dance to break a spell that has been cast over the local theater.
OC can fit into the world - building by being from a new planet or species. For instance, if they are from a planet that has a unique culture based on music, it can add a new aspect to the diverse universe of Guardians of the Galaxy.