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.
In these fanfictions, bounties can also be a source of plot development. For example, a character might be on a quest to increase their bounty to prove themselves. Or, a new and unexpected bounty on a character can lead to all sorts of adventures as they try to figure out why they've been targeted.
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.