One great 'sanji x law fanfiction' is 'The Unlikely Alliance'. It shows an interesting dynamic between the two characters as they team up for a common goal on the high seas. The story has great character development and some really cool action scenes.
Another theme is the mutual respect they develop for each other's skills. Sanji's cooking and Law's medical and strategic abilities are things they come to admire in one another. For example, in many fanfics, Law is initially dismissive of Sanji's cooking but then realizes its value. It's like in 'The Taste of Understanding' fanfic where Law first scoffs at Sanji's food but later it becomes a crucial part of their bond.
One interesting Law x Sanji fanfiction could be where they are forced to team up during a dangerous mission at sea. They start off bickering as usual, but gradually come to respect each other's skills. Law might be impressed by Sanji's cooking, which heals them during their journey, and Sanji might see Law's medical knowledge as useful in more ways than he thought.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions, including many 'sanji x law' ones. The site has a great search function that allows you to filter by tags like 'sanji x law' and other relevant categories.
Well, 'The Culinary Connection' is also a fun fanfic. In this one, Sanji's cooking skills somehow get intertwined with Law's medical knowledge. They end up creating some really unique things together, and along the way, their relationship develops in a very charming way.
Some dedicated One Piece fan forums also have sections for fanfiction. Members often share their own works or recommend good ones they've read. Reddit has some One Piece - related subreddits where people might discuss and link to great Law x Sanji fanfictions. Just be sure to follow the community rules when exploring these sources.
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.
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.