There could be an original character created just for the fanfiction. A woman with a kind heart but a tough exterior, who was a great fighter. She could have met Luffy's father during a battle and they fell in love, and she became Luffy's mother.
She could be a former pirate captain herself. Maybe she was one of the most feared pirates in her time, and her skills and reputation were passed down to Luffy in some way, even if he didn't know it was from his mother.
One idea could be that Luffy's mother was a powerful pirate herself. Maybe she was part of a crew that had a special mission, and she had to give up Luffy to protect him from the enemies she made at sea.
There could be. Fanfiction is a place where all kinds of wild and creative ideas come to life. The idea of fem Harry being Luffy's mother is quite unique and would attract a lot of readers who are into crossovers. Some fanfic writers love to blend different universes together, and this would be a really interesting blend. But finding it might take some time. You should look for fanfics that deal with character relationships in an unconventional way and also check for any tags related to gender - bended characters from the Harry Potter series in the context of One Piece.
Well, perhaps fem Harry travels through different dimensions and lands in the world of One Piece. There, she meets Monkey D. Dragon and they form a relationship. As Luffy's mother, she could have a major influence on his values. She might pass on her sense of justice and determination, which are traits she has from her own story in the Harry Potter universe. The plot could also involve her using her knowledge of magic (or a magical - like power in the One Piece world) to help Luffy's crew during their various challenges. For example, she could help them escape from a powerful enemy's trap by creating some sort of magical diversion. Also, she could be the one who gives Luffy a special item that has magical properties and aids him in his journey to become the Pirate King.
Well, if the Luffy crew were to meet his mother in fanfiction, it could go in many ways. For one, she might be a strong pirate herself. She could then train the crew in new fighting techniques. Or perhaps she has connections all over the world of One Piece and could introduce the crew to important people. It would surely strengthen the bond within the crew as they learn more about Luffy's family.
They would probably be very surprised at first. After all, they might not have expected to ever meet Luffy's mother. Then they would be excited to learn more about Luffy's past from her.
One potential character could be an old friend of Luffy's mother from her celestial dragon days. This friend might have different views now and could either help or hinder Luffy depending on their own motives. Another could be a servant who knew about Luffy's mother's secrets and has been waiting for the right time to reveal them to Luffy.
Well, one possibility could be that Luffy's mother was a celestial dragon who rebelled against their cruel ways. She might have fallen in love with Luffy's father during her journey of self - discovery away from the celestial dragon lifestyle. And then she had to protect Luffy from the wrath of the other celestial dragons as he grew up with his dreams of freedom.
In this fanfiction, it could be that Luffy's mother was thought to be dead but was actually held captive by a powerful enemy. When Luffy finally meets her, she's weak but still full of spirit. She encourages Luffy to keep fighting against the corrupt world of pirates and marines alike. She might also have some inside information about the One Piece, like a clue that she's been holding onto all these years, which sets Luffy on a new and exciting part of his adventure.