Yes, there are quite a few. Some focus on their adventures together, imagining how their different personalities and abilities would interact. For example, a story might have them team up against a powerful new enemy in the One Piece world. They could combine Law's devil fruit powers, Kid's mechanical skills, and Luffy's stretching abilities in unique ways to defeat the foe.
You can start by looking on popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of One Piece fanfictions, and you can easily search for Law x Kid x Luffy stories using the tags and search function. Another option is FanFiction.net, which also has a good number of such fanfictions.
Luffy x Law fanfiction often explores unique relationships. In such works, the interactions between their distinct personalities can be really interesting. Luffy's carefree and bold nature contrasts with Law's more reserved and strategic side. The 'lemon' aspect might add some romantic or tense elements to their relationship, but it also depends on how the author portrays it.
One great fanfiction could be 'The Unlikely Alliance' where Kid, Fem Luffy and Law team up against a new and powerful enemy in the New World. Their interactions are full of bickering at first but then they start to understand each other's motives.
In many fanfictions, the relationships start off rocky. For example, Kid and Law might not trust Fem Luffy's overly optimistic and sometimes reckless nature at first. But as they face challenges together, like fighting a strong pirate crew or dealing with a difficult situation on an island, they start to see her strengths. And Fem Luffy, with her big heart, gradually breaks down the walls that Kid and Law have built around themselves.
A common theme is the exploration of their friendship. Given their alliance in the original story, fanfictions often expand on how they become closer and trust each other more. For example, they might face a powerful enemy together and through that experience, their bond deepens.
One common theme is the exploration of their contrasting personalities. Luffy is so carefree and Law is more reserved. Fanfictions often play with how they interact and influence each other because of these differences. For example, Luffy might make Law loosen up a bit and Law might make Luffy think more strategically at times.
One popular 'law x luffy x kidd fanfiction' might be those that focus on their adventures together in an alternate universe. For example, a story where they team up against a powerful new enemy that the Straw Hats, Heart Pirates, and Kid Pirates would struggle to defeat alone. This could involve a lot of interesting character dynamics as Law's more calculated nature, Luffy's carefree and bold attitude, and Kid's hot - tempered style clash and blend in the face of danger.
I really like 'Luffy and Law's Shared Destiny'. It shows how their fates could be intertwined in a more romantic way. The story has some really sweet moments between them, like when they share their dreams under the starlit sky during a break in their journey. It also adds new elements to the One Piece world they exist in.
One common theme is rivalry. Since both Kid and Law are strong and ambitious characters in their own right, in fanfiction, their rivalry can be explored in different ways, like competing for a certain treasure or goal.