Sure, the One Piece manga is still in the Wano Arc. There are many intense battles and plot twists happening. The arc has been quite elaborate and full of surprises.
One interesting 'One Piece Wano fanfiction' could be about a new character who is a master swordsman from Wano and teams up with Zoro. They go on adventures within Wano, facing off against new and powerful enemies that were not shown in the original story. This could add more depth to the already rich Wano arc.
First, you need to have a good understanding of the One Piece world, especially the Wano arc. Read the manga or watch the anime carefully. Then, think of an interesting concept. It could be a new adventure for the characters, a different outcome for an existing event, or a story centered around a minor character. After that, start creating your characters (if any new ones) and plan out the plot.
In the world of One Piece, there's no indication that the characters themselves watch fanfiction. Fanfiction is a creation of the fans in the real world, and the in - universe characters are too busy with their own adventures, like Luffy chasing after the One Piece, Zoro training to be the world's greatest swordsman, and Nami navigating the seas. They don't have access to or knowledge of the fan - made stories about them.
Yes, it is quite common. 'One Piece' has a huge and passionate fan base. Fanfiction allows fans to explore their creativity and their love for the series in different ways. They can create new adventures for the Straw Hat crew, or explore different relationships between characters. So, a lot of 'One Piece' fans enjoy reading fanfiction to get more of the 'One Piece' world that they love.