One great fanfiction could be about their adventures on a new island not shown in the original story. Maybe they encounter a powerful and strange new enemy. Luffy's determination, Zoro's strength, and Sanji's culinary skills all come into play in this new situation.
One popular type of fanfiction could be adventure - based. Imagine Zoro, Sanji and Luffy finding a mysterious island that has a unique power. Zoro might be the first to face any physical threats on the island, using his three - sword style. Sanji would be there to provide food for the group during their exploration and also use his powerful kicks if needed. Luffy, of course, would lead the way, with his rubber abilities allowing him to reach places others can't and his unwavering determination inspiring the group. This kind of fanfiction often shows the strong bond between the three characters as they face challenges together.
One common theme is their friendship. They are all part of the Straw Hat crew and fanfictions often explore how their different personalities interact and support each other. For example, how Zoro's stoicism and loyalty play off against Luffy's carefree leadership and Sanji's chivalry.
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.
The chemistry between them. Luffy's carefree and determined nature, Zoro's cool and strong - willed self, and Sanji's passionate and sometimes flirty character create a really interesting mix. When they interact in a fanfic, it can lead to some really fun and engaging moments.
Another theme is rivalry. Zoro and Sanji have a friendly rivalry which can be elaborated on in fanfictions. For instance, they might compete in a friendly tournament on the ship to see who is stronger or more useful in a certain situation.
You can start by looking on fanfiction websites like Archive of Our Own. There are often a great number of stories featuring these three characters. Just use their names as search terms and you'll be presented with a variety of options.
There could be a plotline where they get transported to a different dimension. In this new world, Zoro has to learn new sword techniques to fight the strange creatures. Sanji discovers new ingredients and has to adapt his cooking. Luffy befriends some of the locals and together they figure out a way to get back to their own world.
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.
Well, I've read 'The Trio's Unbreakable Alliance' which is a great 'luffy x zoro x sanji fanfic'. It focuses on their growth as a team. Luffy's leadership, Zoro's loyalty, and Sanji's passion are all well - portrayed. It has some really exciting battle scenes where they fight side by side and you can feel the strong bond between them.