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.
One of the most popular death battle scenarios in One Piece fanfiction is the clash between the Straw Hats and the Blackbeard Pirates. It's exciting because both groups have strong and diverse members. Another popular one is a duel between Ace and Akainu re - imagined in a different way than in the original story. Also, battles between the yonko like Kaido and Big Mom are often written in fanfiction as death battles.
In such a fanfic scenario, Luffy's victory would likely depend on the power level and abilities the OC is given. Luffy has his Gum - Gum powers which are extremely versatile. If the OC has some sort of power that can counter Luffy's elasticity, like a power that can solidify or cut through his rubbery body, it could be a tough fight. However, Luffy also has his unwavering determination and the ability to quickly adapt in battles, which often gives him an edge over his opponents.
Well, it could involve the characters from One Piece watching intense death battles between various fighters. Maybe they're commenting on the fighting styles, like Luffy being amazed at some super - fast combatant's moves.