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.
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.
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.
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.
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.
There's also 'Sanji's Secret Admirer'. Here, the OC is a shy girl who has been secretly in love with Sanji for a long time. She leaves little notes and gifts for him. It's a cute story that shows Sanji's charm and how the OC tries to win his heart in her own unique way.
I would recommend 'Three Souls, One Dream'. It has an interesting take on their interactions, showing how Zoro, Luffy, and Sanji grow together as a team. It has some really heartwarming moments that capture the essence of their friendship.
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.
Friendship is a very common theme. Sanji and Luffy have a strong bond, and in fanfictions, this bond is often explored in different situations, like during battles or when they face hardships on their journey.