I haven't really come across many of these, but perhaps themes could include how the crew reacts to such an unexpected situation. Maybe they'd be protective or confused.
Well, common themes could involve the emotional turmoil within Luffy himself. He's always been carefree and now having to deal with pregnancy could bring out new sides of his character. Also, the theme of change in the dynamic of his relationships with his crewmates. Some crewmates might be more helpful, while others might struggle to adjust to the new situation. And then there could be themes related to the future of the Straw Hat Pirates with a pregnant captain, like how they plan for the upcoming changes in their adventures.
A common theme is the exploration of their family relationship. Given that in the original series, their connection isn't delved into much, fanfiction writers often fill this gap. They might write about how Dragon feels about Luffy's growth as a pirate, whether he's proud or worried.
Another theme is the struggle of the pregnant character. In a world full of pirates, marines, and various dangers, being pregnant is not easy. The character may have to deal with physical limitations while still trying to contribute to the crew or their own goals, and this internal and external struggle is often explored in these fanfictions.
One common theme is adventure. Since they are part of the Straw Hat crew in One Piece, fanfictions often put them in new and exciting adventures together. Another theme is growth. Luffy and Robin both grow as characters, and fanfictions explore how they influence each other's growth. For example, Luffy's optimism might help Robin overcome her past traumas.
One common theme is the corruption of innocence. Luffy is usually seen as a very innocent and positive character. But in these fanfictions, his 'dark' side represents the loss of that innocence, often due to some tragic event. Another theme is the struggle for control. He has to fight against this new, dark power within him, trying not to let it completely take over.
One common theme is friendship. Despite their differences, fanfiction often shows them becoming close friends. Another theme is adventure. They might embark on new and dangerous quests together. And power - up themes are also there. Maybe they learn new abilities from each other or find ways to combine their powers for a greater good.
One common theme is friendship. Given Luffy's nature of making strong bonds with people, fanfictions often explore how he and Marco could form a deep friendship. Another theme could be adventure. They are both from the 'One Piece' world which is full of adventures, so fanfictions might create new and exciting adventures for them to go on together.
One common theme is friendship. Luffy and Nami are crewmates, and their friendship is central. Another theme could be protection. Luffy is always ready to protect Nami from danger.
Adventure is also common. They are pirates after all. Fanfictions might take them on new quests or have them explore uncharted islands together, much like in the original series. For example, they could be searching for a hidden treasure that has a special meaning to their family. It's a way to continue the spirit of adventure that One Piece is known for in a new context.
Often, there's the theme of adventure. Since One Piece is an adventure - based story, fanfictions might have Luffy and Reiju going on quests together. Also, themes of loyalty and friendship can be seen. They might have to be loyal to each other in the face of danger. And there can be the theme of self - discovery too. As they interact, they might learn more about themselves. For example, Luffy might learn about more complex family dynamics from Reiju, and Reiju might learn about the simplicity and freedom that Luffy represents.
The theme of acceptance is also present. Hancock has a rather difficult past and her feelings for Luffy make her question a lot of things about herself. Fanfictions will sometimes focus on how Luffy's simple and accepting nature helps Hancock come to terms with her own identity and insecurities, and how she in turn becomes more integrated into Luffy's world.