Mystery is another theme. The concept of a sister dragon in relation to Portgas D Rouge is not fully explored in the original story. Fanfictions can take this opportunity to create mystery around her origin, her powers, and her role in the overall One Piece universe. Writers may introduce hidden secrets and gradually unfold them throughout the story, keeping readers engaged.
A fanfiction could depict Portgas D Rouge as a key figure in a larger story involving Sister Dragon and Luffy's mom. Rouge's sacrifice could have been related to something that Sister Dragon was aware of. Luffy's mom, on the other hand, might have passed on certain powers or knowledge to Rouge before her death. This could lead to a series of events in the fanfiction where Luffy discovers the truth about his mother through the memories and legacies left by Rouge and Sister Dragon.
One possible plot could be that Sister Dragon was an old acquaintance of Portgas D Rouge. They both knew Luffy's mom. Sister Dragon could be on a mission to protect Luffy, as she had made a promise to Luffy's mom long ago. Portgas D Rouge's story of giving birth to Ace could be connected to this overall plot, perhaps there was a threat that they were all trying to prevent that was related to Luffy's future as well.
Fanfiction.net is also a great place. There are many fans who post their works there. However, the quality can vary. You'll need to look through the categories related to One Piece (since Portgas D Rouge is from One Piece) and search for the specific 'Sister Dragon' themed fanfictions. Sometimes, you might find some really interesting ones hidden among a lot of other works.
One common theme is his relationship with his brothers, Luffy and Sabo. There are many fanfictions that explore their childhood memories and how their bond has influenced Ace's life. Another theme is Ace's time in the Whitebeard Pirates. Fanfictions often focus on his interactions with his crewmates and how he grew as a person there.
The most common theme is probably the transformation itself. Writers often focus on how Ace becoming female changes her perspective and the way she approaches life. Power and strength are also themes. Does being female affect her power? Some fanfictions show her having to prove herself more because of her gender. Also, loyalty. Her loyalty to her friends and crew remains a central theme, but it's often explored in new ways due to her new identity as a female in these fanfictions.
Another theme is self - discovery. Ace had a complex identity, being the son of Gol D. Roger. Fanfics often explore how he comes to terms with his heritage and his own place in the world. This can involve his relationships with his adoptive family like Whitebeard and his biological father's legacy.
One common theme is adventure. Since Ace is a pirate in One Piece, many fanfictions incorporate the reader into his exciting adventures on the high seas. They might go on treasure hunts or battle against other pirates together.
One of the main themes is family. Ace's search for his place in the world, considering his complex family background with Gol D. Roger as his father. This theme is often explored in light novels related to him.
Emotional depth is another important aspect. Since Ace has such a complex backstory and relationships, a good fanfiction will explore his emotions. It could be his feelings towards his brothers, his crewmates, or his own identity as a pirate and the son of Gol D. Roger. Also, world - building, if the story takes place in a new location or expands on the One Piece world, should be believable and add to the overall story.
One common theme is adventure. Sonic is known for his speed and love for adventure, and when paired with Rouge, they often embark on exciting quests. For example, in many fanfictions, they might be searching for lost chaos emeralds or trying to stop an evil plan that threatens their world.