One idea could be that the male OC is a former slave who was freed by Whitebeard. He has a deep sense of loyalty towards Whitebeard and is always ready to fight for his newfound family. His unique ability could be related to some form of water - based combat, which is rare in the One Piece world.
First, think about his backstory. For example, he could be an orphan who was taken in by the Whitebeard Pirates. This would give him a strong motivation to protect his new family. Then, consider his skills. Maybe he has a superhuman strength that he uses in battles. Also, his personality is important. He could be a joker in the crew, always making everyone laugh during tough times.
One idea could be an OC who has a unique Devil Fruit ability that helps the Whitebeard Pirates in a crucial battle. For example, a fruit that can manipulate the weather in a small area to their advantage.
First, consider the world of One Piece. The OC should fit within the existing power system. So, if your OC has a special ability, it should be on par with what we've seen in the series. For example, not making them overly powerful without any drawbacks.
Another theme is the search for family. Since Whitebeard's crew is like a big family, the OCs often find a sense of belonging within the crew. They might have had a rough past without a proper family, but with Whitebeard's crew, they finally have a place to call home. This is explored in a lot of fanfictions through the OC's journey of self - discovery and acceptance within the crew.
Well, there could be fanfictions that focus on their epic battles. Maybe ones that explore the backstories of individual crew members in more depth than the original manga or anime. For example, a fanfiction that delves into Thatch's life before joining the crew.
One great 'One Piece Whitebeard OC fanfiction' is 'The Whitebeard's New Heir'. It has an interesting OC who is a young pirate with a special ability and joins Whitebeard's crew. The story is full of action and adventure as they face off against other pirates.
Fanfictions that give more screen time to the less - known members of the Whitebeard Pirates. These stories could be popular among fans and also interesting for the crew themselves. They might enjoy seeing how fans view and develop the characters who don't always get as much focus in the official story.
One interesting Whitebeard Pirates fanfiction could be about a new crew member joining them. This new member has a unique power that the crew has never seen before and they have to figure out how to incorporate it into their battles and daily life on the ship.
Whitebeard himself is often a very popular character in fanfiction. His powerful presence and fatherly role in the crew make him a central figure. Writers can explore his leadership, his past battles, and his relationships with the other crew members.