Yes, there might be some. You can try searching on popular fanfiction websites like Archive of Our Own or FanFiction.net. However, the availability can vary greatly depending on how active the 'One Piece' fanfiction community is in writing such stories.
One common theme could be the reactions of the other Straw Hat crew members. They might be shocked, happy, or worried. Another theme could be how Sanji and Nami deal with the situation, like Sanji becoming overly protective or Nami being concerned about her future as a pirate while being pregnant.
For Nami, her intelligence and cunning are key. She could use her smarts to get Sanji out of trouble in the fanfiction. Also, her love for money and treasure can add an interesting dynamic. For example, she might convince Sanji to go on a dangerous adventure in search of a valuable item, promising him new ingredients for his kitchen.
One interesting plot twist could be that the pregnancy is a result of some sort of magical or strange One Piece - world - related phenomenon rather than the usual way. Maybe they were exposed to a devil fruit - related effect that caused it. Another could be that they initially keep it a secret from the rest of the crew for various reasons, like fear of how Luffy might react. This secrecy could lead to a lot of comical or tense moments as they try to hide the signs of pregnancy.
Love and attraction are very common themes. Sanji is often depicted as being head - over - heels for Nami, and his pursuit of her is a central part of many fics.
In nami and sanji fanfiction, the theme of admiration is quite common. Sanji admires Nami's beauty and intelligence, and Nami may come to admire Sanji's loyalty and cooking skills. Another theme is the idea of finding a home or a family. They are both part of the Straw Hat crew, and their relationship can be seen as a part of that family - like bond. Additionally, the theme of facing challenges together, whether it's pirates or other obstacles, and how this strengthens their relationship.
It can be developed through shared hobbies in the modern world. For instance, if they both like extreme sports, they could bond over skydiving or surfing. This would not only bring them closer but also show a different side of their characters.
One common theme is unrequited love at the start. Often, Sanji has strong feelings for Nami while she is initially oblivious or not fully receptive. Another theme is the idea of protection. Sanji is always eager to protect Nami, whether it's from other pirates or just general dangers. For example, in many fanfictions, when the crew is in a fight, Sanji will put himself in harm's way to keep Nami safe.
One interesting Sanji and Nami fanfiction could be about them going on a special adventure together. Maybe they end up on a deserted island and Sanji has to use his cooking skills to find food while Nami tries to figure out how to signal for help. Another could be a story where Sanji creates a special meal just for Nami to cheer her up after a tough battle.
The theme of unrequited love that slowly turns into mutual love is also quite common. At first, Sanji might be more openly in love while Nami is focused on other things like treasure or mapping. But over time, through shared experiences and Sanji's consistent care, Nami realizes her own feelings for him, and this transformation is a major aspect in many fanfictions.