Yes, there are likely some out there. Fanfiction often explores unique crossovers like this. You can check fanfiction websites such as Archive of Our Own or FanFiction.net to find them.
One interesting Trafalgar Law OC fanfiction could be one where the OC is a doctor on his ship, adding a new dynamic to the medical team. They might have a unique backstory that ties into Law's past in some way.
One great Trafalgar Law time travel fanfiction is 'Law's Time - Bound Voyage'. It has an interesting plot where Law travels back in time and tries to change certain events in the One Piece universe. The story is well - written and the author does a great job of staying true to Law's character.
It could be really strange yet interesting. Maybe Naruto would have Law's powers and his calm, calculating demeanor. He might use Law's Room ability in the Naruto universe during battles.
A crossover with 'Bleach' could be really cool. Law could end up in the Soul Society and his powers would be a mystery to the Shinigami. His ability to create 'Rooms' and manipulate objects within them could be seen as a threat or a new form of spiritual power. He might also get involved in the battles between the Soul Reapers and the Hollows, bringing his own brand of justice and strategy.
First, decide which universe you want to cross Law with. Then, think about how Law would fit into that world. For example, if it's a 'Harry Potter' crossover, consider how his powers would interact with magic. Next, come up with a basic plot. It could be something like Law is on a mission in the wizarding world to find a powerful magical artifact. Then start writing an engaging opening, like Law suddenly appearing in Diagon Alley and causing a stir.
One common theme is rivalry - turned - friendship. Since they are both pirates in One Piece, their initial relationship as rivals can develop into something more friendly or even romantic in fanfiction. Another theme is adventure. Writers often create new adventures for them to go on together. Team - up is also a popular theme, where they join forces against a common enemy.
Websites like Archive of Our Own (AO3) are great places to start. There are a large number of fanfictions there, and you can use the search function to specifically look for Trafalgar Law OC fanfictions. You can also filter by things like rating and word count to find the ones that suit your taste.
One common theme is adventure. Since they are both from the One Piece world which is full of adventures, fanfictions often put them in new and exciting adventures together. They might explore uncharted islands or face new and powerful enemies.
Another trope is the 'meeting past self' scenario. This can be really interesting as Law has to deal with his own younger self, either trying to guide him or hiding his true identity. It often leads to some self - reflection on Law's part and some great character development moments.