Perhaps in this fanfiction, Naruto is on a mission in his own world when a strange portal opens and leads him to the One Piece universe right where Robin is. At first, they are both cautious of each other. But as they learn about their respective powers and goals, they decide to join forces. Maybe there's a common enemy that is threatening both the ninja world and the pirate world, and together they strive to defeat it.
Another interesting one is 'Luffy and Robin's Secret Journey'. This fanfic focuses on their personal growth while on a journey that only the two of them embark on. It shows how they start to understand each other on a deeper level, and how their relationship blossoms over time. Luffy's simple yet profound view of the world and Robin's complex past form an engaging contrast.
One good fanfiction could be 'The Law and Robin Alliance' which focuses on their adventures together and how their skills complement each other. It has a great plot that shows their growing bond as they face various challenges in the One Piece world.
It could be a powerful ninja from Naruto's world who has turned evil and has found a way to travel to the One Piece world. He wants to use the power of the Devil Fruits and the ancient secrets Robin knows to take over both worlds.
A highly recommended one is 'The Law - Robin Connection'. This fanfiction explores the backstories of both characters and how those past experiences bring them closer together. It's not just about their relationship but also about their individual growth within the context of the One Piece universe. There are some great character - building moments and a really engaging storyline.
Their relationship could start with distrust. Aokiji being a former Marine and Robin being a wanted archaeologist. But as they interact more, they might find common ground in their search for truth. Maybe they start to share stories about their pasts, which slowly builds a bond between them.
I like the storylines where Robin forms deep friendships in the fanfictions. In one, she befriends a group of scholars on an island. They exchange knowledge and she helps them protect their research from pirates. It's a great display of her character values. There are also storylines that explore her relationship with the other Straw Hats in new ways, like how she teaches Usopp about ancient plants.
You can start by looking on fanfic websites like Archive of Our Own (AO3) or Fanfiction.net. Just type in 'One Piece Luffy x Robin' in the search bar and you'll get a list of relevant fanfics.
One common theme is adventure. Since One Piece is all about the grand adventure, fanfictions often continue this. Luffy, Nami and Robin go on new and exciting quests together. Another theme is friendship. Their relationships are explored in depth, showing how they rely on and support each other. And sometimes, there's the theme of self - discovery. Nami might discover new aspects of her courage, Robin could learn more about her past through their adventures, and Luffy could find new ways to lead the crew.
One idea could be that the OC is a long - lost relative of a Straw Hat member. For example, an OC who is related to Luffy and has a unique power of their own, like the ability to control the weather in a small area. This could lead to interesting storylines where the OC helps the crew during difficult battles or in traversing dangerous seas.